Slight Misalignment Research Articles

Numerical simulation of the effect of angular misalignment on the dynamic behaviour of bearing

Bearing has been used extensively in numerous applications and their unplanned failure has a consequential effect on the smooth operation of the machinery. A slight misalignment in bearing has a detrimental effect on the smooth running of most machines. Hence, the paper leverages finite element technique to simulate the consequential effect of different degrees (0.1°, 0.2°, 0.3°, 0.4°, 0.5°) of misalignment on the dynamic behaviour of a cylindrical roller bearing subjected to typical operating conditions of an airflow root blower. The results of the study show that during operation, the temperature and Hertzian stress developed increased with an increase in the degree of misalignment and operating/rotating speed, and the maximum Hertzian stress was developed on the outer ring of the bearing in all the degrees of misalignments and operational speeds considered. Thus, making the outer ring of the bearing component, the most prone to failure during operation in the presence of misalignment.

Cycle-Generative Adversarial Network-Based Image Correction of 4-Dimensional Cone-Beam Computed Tomography for Lung Cancer Adaptive Radiation Therapy

To achieve high-precision stereotactic body radiotherapy, visualization of moving tumor/target estimation is performed using 4-dimensional cone-beam computed tomography (4D-CBCT) before each treatment fraction. Currently, respiration-correlated 4D-CBCT is achieved with subgroups of cone-beam projections into different respiratory phases. However, insufficient projections inside each phase bin cause severe imaging artifacts. Convolutional neural networks are widely used to correct CBCT specific artifacts. Previous research has shown that mean absolute error in Hounsfield units improved up to 93% over the original CBCT image. However, slight voxel-wise misalignment between the training images may lead to blurred synthesis, and hence, due to respiratory motion, it is impossible to perform 4D-CBCT imaging without organ misalignment with the 4D-computed tomography (4D-CT). Cycle-generative adversarial network (cycle-GAN) framework enforces an inverse transformation and achieves high accurate consistency even in mapping nonlinear domains. The aim of this study was to improve 4D-CBCT image quality using cycle-GAN and evaluate its use in adaptive radiation therapy (ART) planning for lung cancer.Unpaired 4D-CT and 4D-CBCT taken from publicly available datasets in 5 patients who underwent lung cancer treatment were used for training using cycle-GAN model. Then, Synthesis of 4D-CBCT (Syn-CBCT) images with improved quality conferred by the cycle-GAN model was tested in another 5 cases in the lung region. To assess pixel value deviation and image similarity, mean absolute errors (MAE) and structural similarity index measure (SSIM) were calculated for Syn-CBCT and paired 4D-CT images and compared with those of original 4D-CBCT images. Moreover, volumetric modulation arc therapy plans with a dose of 48 Gy in 4 fractions were recalculated based on Syn-CBCT images, and 3-dimensional (3D)-gamma (3%/3 mm) analysis was conducted to compare the former with ideal dose distributions observed in 4D-CT images.4D-CBCT imaging quality was improved and lung tumor regions were clearly observed after noise and artifact removal by applying the trained cycle-GAN model. MAEs were improved by 21% and SSIMs by 46% for whole images. Hence, pixel value and structural visualization in Syn-CBCT images could achieve near-ideal quality of 4D-CT images. Large structures were generally consistent with those in paired 4D-CT images, whereas fine structures (pulmonary vessels and fine bones) were not completely duplicated. However, a mean 3D gamma pass rate of > 95% was achieved in all cases.The proposed cycle-GAN method enhances 4D-CBCT image quality, making it comparable to that of 4D-CT images. Thus, clinical implementation of Syn-CBCT-based ART is feasible.

Laboratory measurements with DAS: A fast and sensitive tool to obtain elastic properties at seismic frequencies

Forced-oscillation stress-strain laboratory measurements are increasingly employed to obtain elastic and viscoelastic properties of rocks at seismic frequencies. Yet these measurements are time-consuming and expensive, due in part to the use of metal or semiconductor strain gauges, which need to be glued to the sample. Such gauges are fragile, have relatively low sensitivity, and measure very local strain only so the measurements can be affected by a slight misalignment of the system assembly and local heterogeneity of the rock. The emergence of fiber-optic distributed acoustic sensing (DAS) technology provides an alternative means of measuring strain. Strain measurements with DAS involve winding an optical fiber around the sample multiple times and connecting it to a DAS recording unit. Pilot experiments performed using this setup on a range of rocks and materials show good agreement with strain gauge measurements. Advantages of DAS over strain gauges include much higher strain sensitivity (down to 10−11) and signal-to-noise ratio (and hence, shorter time required for measurements), larger dynamic range, ability to measure average (rather than local) strain in the sample, and robustness at elevated temperatures. Although the pilot experiments demonstrate the potential of DAS for rock physics measurements, further research and improvement of the proposed methodology are required to obtain independent estimates of Young's modulus and Poisson's ratio and to port the system into a pressure vessel to obtain rock properties under in-situ conditions.

Use of color based chromatographic images obtained from comprehensive two-dimensional gas chromatography in authentication analyses

Comprehensive two-dimensional gas chromatography (GC×GC) has been an important technique used to acquire as much information as possible from a wide variety of samples. Qualitative contour plots analysis provides useful information and in daily use it ends up being handled as images of the volatile organic compounds by analysts. Cachaça samples are used in this paper to showcase the use of two-dimensional chromatographic images as the main source for authentication purposes through one-class classifiers, such as data-driven soft independent modeling of class analogy (DD-SIMCA). The proposed workflow summarizes this fast and easy process, which can be used to certify a specific brand in comparison to other brands, as well as to authenticate if samples have been adulterated. Lower quality cachaças, non-aged cachaças and cachaças aged in different wooden barrels were tested as adulterants. Chromatographic images allowed for the distinction of all brands and nearly every adulteration tested. Sensitivity was estimated at 100% for all models and specificity ranged from 96% to 100%. Different approaches were used, alternating from working with whole-sized images to working with smaller resized versions of those images. Resized chromatographic images could be potentially useful to easily compensate for slight chromatographic misalignments, allowing for faster calculations and the use of simpler software. Reductions to 50% and 25% of the original size were tested and the results did not greatly differ from whole images model. As such, 2D chromatographic images have been found to be an interesting form of evaluating a product's authenticity.

How Signaling Geometry Shapes the Efficacy and Evolution of Animal Communication Systems.

Animal communication is inherently spatial. Both signal transmission and signal reception have spatial biases-involving direction, distance, and position-that interact to determine signaling efficacy. Signals, be they visual, acoustic, or chemical, are often highly directional. Likewise, receivers may only be able to detect signals if they arrive from certain directions. Alignment between these directional biases is therefore critical for effective communication, with even slight misalignments disrupting perception of signaled information. In addition, signals often degrade as they travel from signaler to receiver, and environmental conditions that impact transmission can vary over even small spatiotemporal scales. Thus, how animals position themselves during communication is likely to be under strong selection. Despite this, our knowledge regarding the spatial arrangements of signalers and receivers during communication remains surprisingly coarse for most systems. We know even less about how signaler and receiver behaviors contribute to effective signaling alignment over time, or how signals themselves may have evolved to influence and/or respond to these aspects of animal communication. Here, we first describe why researchers should adopt a more explicitly geometric view of animal signaling, including issues of location, direction, and distance. We then describe how environmental and social influences introduce further complexities to the geometry of signaling. We discuss how multimodality offers new challenges and opportunities for signalers and receivers. We conclude with recommendations and future directions made visible by attention to the geometry of signaling.

Removing Phase Misalignment in the Validation of a Compact Antenna Test Range for 5G mm-Wave UE OTA Testing

Over-the-air (OTA) measurement is mandatory for 5G mm-wave wireless devices. The compact antenna test range (CATR) is the baseline method in the current version of TR 38.810 in 3rd generation partnership project (3GPP) and cellular telecommunications industry association (CTIA) millimeter-wave (mm-Wave) test plan. For CATR, both amplitude and phase variations inside the quiet zone (QZ) could affect the final OTA results significantly and hence need to be characterized carefully. Especially in the phase validation of QZ, even slight misalignments between sampling plane and incident plane wavefront due to the limited precision of the positioner or tolerance in antenna fixture could result in large phase variations, which is not the true phase property of QZ. This letter presents a method to remove the effect of the angular error due to misalignment when measuring the phase variation inside QZ. By adopting the proposed method to the measured phase data, any angular error due to misalignment with respect to the incident plane wavefront will be eliminated mathematically, leaving the true phase variations of QZ only. In the meanwhile, the proposed method can alleviate the requirements of fixture manufacture and alignment precision and reduce the test cost.

Numerical estimation of errors in drop angle during drop tests of IP-Type metallic transport containers for radioactive materials

For industrial package (IP)-type transport containers for radioactive materials, a free drop test should be conducted under regulatory conditions. Owing to various uncertainties observed during the drop test, errors in drop angles inevitably occur. In IP-type metal transport containers in which the container directly impacts onto a rigid target without any shock absorbing materials, the error in the drop angle due to a slight misalignment makes a significant difference from the ideal drop. In particular, in a vertical drop, the error in the drop angle causes a strong secondary impact. In this paper, a numerical method is proposed to estimate the error in the drop angle occurring during the test. To determine this error, an optimization method accompanying a computational drop analysis is proposed, and a surrogate model is introduced to ensure calculation efficiency. Effectiveness of the proposed method is validated by performing the verification and comparison between the test and the analysis applied with the drop angle error.

Miscalibration-Tolerant Fourier Ptychography

Fourier Ptychography probes the sample from different directions to achieve label-free quantitative phase imaging with a large space-bandwidth product. However, special attention has to be paid in the calibration of the optical setup to assure the accurate knowledge of the geometrical parameters involved in the image reconstruction. Any slight misalignment can provoke incorrect synthesis of the observables and, in turn, severe phase errors in the resulting high-resolution image. Here, we present a new processing pipeline that automatically removes such a priori unknown artifacts, thus making Fourier Ptychography miscalibration-tolerant. This result is achieved through a numerical Multi-Look approach that generates and combines multiple reconstructions of the same set of observables where phase artifacts are largely uncorrelated and, thus, automatically suppress each other. The proposed method is non-iterative, fully parallelizable, and completely blind, unlocking the use of Fourier Ptychography as an easy to handle tool or add-on to existing microscopes to be employed by unskilled users, thus paving the way to biomedical and clinical practices.

Severe Ankle Varus Malalignment Management with a Fix-Bearing Total Ankle Replacement Implant

Category:Ankle Arthritis; AnkleIntroduction/Purpose:Despite Total ankle replacement (TAR) is currently considered a safe procedure and an optimal alternative to ankle fusion in end-stage ankle arthritis, still the precise indications and the limits of TAR are a highly controversial topic. Coronal malalignment correction with TAR is also a widely debated point. Purpose of this work was to confront two patient groups undergoing Total Ankle Replacement (a group of patients with a pre-operative ankle varus misalignment on coronal plane, versus a group of patients with neutral pre-operative ankle alignment) comparing clinical and radiographic results, complications and survival rate of the implant.Methods:171 patients, all affected by end-stage ankle arthritis and all treated with total ankle replacement with fix-bearing Trabecular Metal Total Ankle System (Zimmer-Biomet, Warsaw IN, USA), were divided in two groups. Group ‘A’ included 159 patients having a normal alignment or a slight valgus or valgus misalignment within 10°. Group ‘B’ included 12 patients with a pre- operative varus malalignment >10°. Each patient of the study was evaluated, clinically and radiologically, before and after surgery, and subsequently at 6 and 12 months follow-up, then once every year. Clinical evaluation comprised some score: visual analogue scale (VAS); American Foot and Ankle Society Score (AOFAS); and the Short Form (SF)-12 Quality of Life, in both of its ‘physical’ (PCS) and ‘mental’ (MCS) components. Radiological evaluated parameters were: tibio-talar surface angle (TTS), lateral distal tibial angle (LDTA-α), and anterior distal tibial angle (ADTA-β). Complications and implant survival rate were evaluated for both groups.Results:At a mean follow up of 2,75 years (range 2.09-5.66 years), improvement was found in all clinical and radiological evaluated parameters of two groups, without statistically significant differences between two groups at last follow-up. In group A most frequent reported complication was the presence of a fibular symptomatic hardware. Major complication were a deep arthroplasty infection and a 3 months post-operative ankle fracture-dislocation/periprostethic fracture. In group B there were 2 delayed wound healing, and one case of loosening of correction. No significant difference in complication and revision rate comparison between two groups was founded.Conclusion:Mid-term results reported in the present show that in patients with varus greater than 10 ° it is possible to obtain a post-operative alignment similar to pre-operative neutral ankles and that the complication rate is not greater. Despite this, is Authors opinion that major and complex misalignment should be approached by skilled surgeons, with an adequate learning curve experience, with a wide range of cases and in highly specialized centers.

Buckling study on Two-Stage absorption energy coupler

A two-stage absorption energy structure composed of an expanding tube and a buffer has been conventionally applied to the couplers of the China Railway High-speed system. Previous investigations have revealed the energy-absorption characteristics of the couplers. However, in dynamic experiments, some of the couplers were found to buckle at the expansion cone. To analyse the buckling problem of the couplers, a simple theoretical model was established and verified via the finite element method (FEM) and experiments. The critical conditions for the couplers buckling and the bending strengths of the expansion tubes were studied. The results indicate that a slight initial misalignment between the expansion cone and outer tube can cause buckling of the couplers. Further, the stabilities of expansion tubes can be significantly improved by increasing the contact area of the expansion cone, reducing the length of expansion tubes, maintaining separation between the expansion cone and the midpoint of the couplers, and increasing the stiffness of expanding tubes. This study is expected to provide guidelines for solving the stability problems of long-stroke expansion tubes and advances the design of such expansion tubes.

Image-Based Inertial Impact (IBII) Tests for Measuring the Interlaminar Shear Moduli of Composites

The image-based inertial impact test has previously shown that inertial effects generated with high-strain-rate loading can be used to measure the dynamic constitutive properties of composites at strain rates on the order of 1600,{rm s}^{-1}. This work represents an important next step in exploring the potential of this concept with two tests presented where loading heterogeneity is exploited to measure the interlaminar shear modulus and stress–strain behaviour at high strain rates. The first test configuration used a short-beam with asymmetric loading to activate the shear behaviour. The virtual fields method was used to directly identify the interlaminar shear modulus from heterogeneous full-field maps of strain and acceleration. Simulated experiments were used to optimise the test configuration, select optimal smoothing parameters, and quantify uncertainty from grid rotation on the shear modulus identifications. The test was validated experimentally with three different virtual fields identifying an average shear modulus ranging from 5.7 to 5.9 GPa measured at 1600,{rm s}^{-1}, representing a 16–19% increase compared to quasi-static measurements. The shear modulus could also be identified from shear introduced into specimens tested in the standard, end-on interlaminar IBII configuration from slight in-plane misalignments of the impactor. The identified value of 5.6 GPa validates measurements from the first configuration and also demonstrates the capability to identify multiple interlaminar stiffness parameters from a single test.

Generation of an X-ray nanobeam of a free-electron laser using reflective optics with speckle interferometry.

Ultimate focusing of an X-ray free-electron laser (XFEL) enables the generation of ultrahigh-intensity X-ray pulses. Although sub-10 nm focusing has already been achieved using synchrotron light sources, the sub-10 nm focusing of XFEL beams remains difficult mainly because the insufficient stability of the light source hinders the evaluation of a focused beam profile. This problem is specifically disadvantageous for the Kirkpatrick-Baez (KB) mirror focusing system, in which a slight misalignment of ∼300 nrad can degrade thefocused beam. In this work, an X-ray nanobeam of a free-electron laser wasgenerated using reflective KB focusing optics combined with speckle interferometry. The speckle profiles generated by 2 nm platinum particles were systematically investigated on a single-shot basis by changing the alignment of the multilayer KB mirror system installed at the SPring-8 Angstrom Compact Free-Electron Laser, in combination with computer simulations. It was verified that the KB mirror alignments were optimized with the required accuracy, and a focused vertical beam of 5.8 nm (±1.2 nm) was achieved after optimization. The speckle interferometry reported in this study is expected to be an effective tool for optimizing the alignment of nano-focusing systems and for generating an unprecedented intensity of up to 1022 W cm-2 using XFEL sources.

Parameters of the Earth\u2019s Free Core Nutation from Diurnal Strain Tides

Earth deformation at the diurnal tidal frequencies includes the resonant tidal-forcing response caused by the Free Core Nutation (FCN), a retrograde mode related to the slight misalignment of the rotation axes of the outer core and mantle. We analyse data from four underground high-sensitivity laser extensometers, whose signal-to-noise ratio in the diurnal tidal band is particularly high, and provide an alternative independent estimate of the FCN complex frequency with respect to more usual techniques (nutation and gravity). Firstly, we differentiate displacements due to diurnal solid tides to obtain extension along any azimuthal direction in terms of three complex parameters (A, S, C) which depend on latitude and frequency. Then, we demonstrate that we can invert the FCN complex frequency and the sensitivity of Im(A) and Re(S) to the resonance from our data. Lastly we obtain the probability distributions of those four parameters. Our results are in full agreement with those from nutation and gravity, as well as with reference IERS (International Earth Rotation and Reference Systems Service) values. Sensitivities of Im(A) and Re(S) to the resonance are estimated here for the first time and are in agreement with values computed using reference Love and Shida numbers from IERS.

Scale distortion correction of a digital micromirror device using diffraction caustics

A Digital Micromirror Device or DMD is an instrument used to encode information on a light beam by modulating its amplitude. This device is composed of an array of tiny mirrors that can be controlled individually and can thus act as binary apertures to control the amplitude of light. DMD’s with a diamond pixel configuration have stretching distortion to the uploaded patterns. Although the patterns can be rescaled before uploading to the DMD, there is no straightforward method to determine the proper scaling factor. Here, we propose a method to find the scaling factor for the DMD by looking at diffraction caustics. We uploaded elliptical slits in the DMD that results in astroids caustics which collapse to a point when the correct scaling is matched. The scaling factor we found corrects both the inherent distortion caused by the DMD and the distortion caused by a slight misalignment of the DMD. This method offers a faster and more sensitive determination of the scale ratio instability of diffraction catastrophes and the very nature of diffraction. This method can be used to determine aspect ratios of other similar devices especially when these devices use differently shaped mirrors or when the device’s orientation is constrained such that when it is tilted.

A Fast and Flexible Projector-Camera Calibration System

Existing projector-camera calibration methods typically warp keypoints from a camera image to a projector image using estimated homographies and often suffer from errors in camera parameters and noises due to imperfect planarity of the calibration target. This article proposes a practical and robust projector-camera calibration system that explicitly deals with these challenges. First, a graph-theory-based correspondence algorithm is built on top of a color-coded spatial structured light (SL) pattern. Such SL correspondences are then used for a coarse projector-camera calibration. To gain more robustness against noises from an imperfect planar calibration board, we develop a bundle adjustment algorithm to jointly optimize the estimated projector-camera parameters and the correspondences’ coordinates. Moreover, our system requires only one shot of an SL pattern for each calibration board pose, which is much more practical than multishot solutions. Comprehensive experimental validation is conducted on both synthetic and real data sets, and our method clearly outperforms the existing methods in all experiments. For the benefit of the society, a practical open-source software with graphical user interface (GUI) of the developed system is publicly available at <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><uri>https://github.com/bingyaohuang/single-shot-pro-cam-calib</uri></monospace> . <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —The proposed method is motivated by two challenges in industrial structured light (SL) system calibration: 1) robustness against imperfect planarity of the calibration target and 2) the number of SL projections per pose. In many industrial SL-based 3-D reconstruction systems, the calibration accuracy greatly affects the reconstruction reliability. Our SL calibration system explicitly deals with calibration target’s imperfect planarity and thus outperforms the existing methods in terms of system accuracy. Another advantage of our SL calibration system is single-shot-per-pose, allowing fast recalibration and reducing the decoding error due to slight pattern misalignment in multishot methods <xref ref-type="bibr" rid="ref37" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[37]</xref> . In addition, we release the open-source calibration software with a graphical user interface (GUI), with which calibration and sparse 3-D reconstruction can be easily performed without any further instructions. Moreover, considering the complex calibration environment and setup, we make the camera and projector imaging parameters, such as exposure, brightness, and contrast, adjustable through widgets and preview. Finally, a limitation of our color-coded SL system is its sensitivity to environment lighting and target texture. This problem may be solved by projector photometric compensation <xref ref-type="bibr" rid="ref16" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[16]</xref> , <xref ref-type="bibr" rid="ref18" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[18]</xref> , <xref ref-type="bibr" rid="ref19" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[19]</xref> , <xref ref-type="bibr" rid="ref39" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[39]</xref> .

Three-dimensional high resolution topology optimization considering additive manufacturing constraints

This paper studies additive manufacturing oriented structural topology optimization with SIMP approach and aims at 3D high-resolution printable structural topology design with overhang and horizontal minimum length control for minimum compliance.To start with, we construct a hyperplane in ℝ4 by fitting a local element density distribution in the 18 Elements Scheme, use its gradient to estimate the overhang angle, the directional-dependent overhang angle and formulate the corresponding constraints. Next, we propose a Horizontal Square Scheme and four support sets around the concerned element. The horizontal minimum length is controlled by forbidding the concerned element’s density to be larger than the average density of the elements in one of the support sets. By combining these two constraints, the hanging feature is well suppressed.A new implementation scheme with an improved weight function is proposed to meet these element wise AM constraints well. To get high resolution structural boundaries with low computational efforts, this paper applies the multiresolution topology optimization (MTOP) method.The structural TO problem is solved by MMA. A number of numerical examples and AM experiments show the effectiveness of this method. The present approach works efficiently when the building direction is in slight misalignment with the vertical direction.

Digital volume correlation technique for characterizing subsurface deformation behavior of a laminated composite

In the present study, the digital volume correlation (DVC) technique is used to study the deformation behavior occurring inside a carbon fibre-reinforced epoxy composite. While a tensile test on a symmetric angle-ply laminated composite specimen is being performed, X-ray images are recorded using synchrotron radiation. The radiographs are processed to reconstruct 3D μCT images. The reconstruction process utilizes a filtered back-projection (FBP) algorithm combined with a phase retrieval method to enhance the contrast of the CT images. Phase contrast is crucial since the natural microstructural pattern is analogous to a speckle pattern for digital image correlation (DIC) analysis. A slight misalignment of the specimen, typically negligible at the macroscopic scale, is corrected in the CT images prior to the DVC analysis. The accuracy of the DVC results is improved by implementing a sub-voxel registration approach to achieve a resolution less than one pixel. The DVC results are compared with finite element analysis (FEA) results. Although the overall results agree well with the FEA results, few subvolumes are prone to fail to find their correct pairs within DVC volumes. Raw 2D tomograms are individually examined and compared to show that a high correlation coefficient value does not always guarantee a correct match. Detailed discussions about the misleading correlations are provided and thereby the validations and limitations of the DVC (and DIC) technique are addressed.

Radially polarized symmetric Airy beam.

In this Letter, we introduce a new kind of radially polarized beam called the radially polarized symmetric Airy beam (RPSAB). Compared to the linearly polarized symmetric Airy beam (SAB), the hollow focus spot of RPSAB enables it to trap a microparticle whose refractive index is lower than that of the surrounding medium, and the focus intensity of RPSAB is nearly three times higher than that of SAB under the same conditions. Also, we present the on-axis and off-axis radially polarized symmetric Airy vortex beam (RPSAVB). In the on-axis case, we find the maximum intensity of RPSAVB is about two times higher than that of RPSAB. For the off-axis case, we prove that slight misalignment of the vortex and RPSAB enables guiding the vortex into one of the self-accelerating channels, the same as the symmetric Airy vortex beam. Our results may expand the applications of RPSAB in laser cutting, metal processing, nanofocusing, and three-dimensional trapping of metallic Rayleigh particles.

Robotilter: an automated lens/CCD alignment system for the Evryscope

Camera lenses are increasingly used in wide-field astronomical surveys due to their high performance, wide field-of-view (FOV) unreachable from traditional telescope optics, and modest cost. The machining and assembly tolerances for commercially available optical systems cause a slight misalignment (tilt) between the lens and CCD, resulting in point spread function (PSF) degradation. We have built an automated alignment system (Robotilters) to solve this challenge, optimizing four degrees of freedom—two tilt axes, a separation axis (the distance between the CCD and lens), and the lens focus (the built-in focus of the lens by turning the lens focusing ring, which moves the optical elements relative to one another) in a compact and low-cost package. The Robotilters remove tilt and optimize focus at the sub-10-μm level, are completely automated, take ≈2 h to run, and remain stable for multiple years once aligned. The Robotilters were built for the Evryscope telescope (a 780-MPix 22-camera array with an 8150-sq. deg FOV and continuous 2-min cadence) designed to detect short-timescale events across extremely large sky areas simultaneously. Variance in quality across the image field, especially the corners and edges compared to the center, is a significant challenge in wide-field astronomical surveys like the Evryscope. The individual star PSFs (which typically extend only a few pixels) are highly susceptible to slight increases in optical aberrations in this situation. The Robotilter solution resulted in a limiting magnitude improvement of 0.5 mag in the center of the image and 1.0 mag in the corners for typical Evryscope cameras, with less distorted and smaller PSFs (half the extent in the corners and edges in many cases). We describe the Robotilter mechanical and software design, camera alignment results, long-term stability, and image improvement. The potential for general use in wide-field astronomical surveys is also explored.

Robotilter: An automated lens/CCD alignment system for the Evryscope

Camera lenses are increasingly used in wide-field astronomical surveys due to their high performance, wide field-of-view (FOV) unreachable from traditional telescope optics, and modest cost. The machining and assembly tolerances for commercially available optical systems cause a slight misalignment (tilt) between the lens and CCD, resulting in PSF degradation. We have built an automated alignment system (Robotilters) to solve this challenge, optimizing 4 degrees of freedom - 2 tilt axes, a separation axis (the distance between the CCD and lens), and the lens focus (the built-in focus of the lens by turning the lens focusing ring which moves the optical elements relative to one another) in a compact and low-cost package. The Robotilters remove tilt and optimize focus at the sub 10 micron level, are completely automated, take 2 hours to run, and remain stable for multiple years once aligned. The Robotilters were built for the Evryscope telescope (a 780 MPix 22-camera array with an 8150 sq.deg. field of view and continuous 2-minute cadence) designed to detect short timescale events across extremely large sky areas simultaneously. Variance in quality across the image field, especially the corners and edges compared to the center, is a significant challenge in wide-field astronomical surveys like the Evryscope. The individual star PSFs (which typically extend only a few pixels) are highly susceptible to slight increases in optical aberrations in this situation. The Robotilter solution resulted in a limiting magnitude improvement of .5 mag in the center of the image and 1.0 mag in the corners for typical Evryscope cameras, with less distorted and smaller PSFs (half the extent in the corners and edges in many cases). In this paper we describe the Robotilter mechanical and software design, camera alignment results, long term stability, and image improvement.