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Applying the iterative stitching algorithm, we demonstrate the power of subaperture testing through experiments. Naturally the algorithm applies to flats, spherical or aspheric surfaces. We first apply it to a silicon carbide flat mirror with larger aperture than the interferometer's. The testing results help to obtain a high-precision mirror through five iterations of ion beam figuring. The second experiment is 37-subaperture testing of a large spherical mirror. Good consistence is observed between the stitching result and the full aperture test result using a Zygo interferometer. Finally we study the applicability of the algorithm to subaperture testing of a parabolic surface. The stitching result is consistent with the auto-collimation test result. Furthermore, the surface is tested with annular subapertures and also retrieved by our algorithm successfully.

Real-time localization is an important mission for self-driving cars and it is difficult to achieve precise pose information in dynamic environments. In this paper, a novel localization method is proposed to estimate the pose of self-driving cars using a 3D-LiDAR sensor. First, the multi-frame curb features and laser intensity features are extracted. Meanwhile, based on the high-precision curb map generated offline, obstacles on road are detected using region segmentation methods and their features are removed. Furthermore, a map-matching method is proposed to match the features to the map, a robust iterative closest point algorithm is utilized to deal with curb features along with a probability search method dealing with intensity features. Finally, two separate Kalman filters are used to fuse the low-cost global positioning systems and map-matching results. Both offline and online experiments are carried out in dynamic environments and the results demonstrate the accuracy and robustness of the proposed method. [ABSTRACT FROM AUTHOR]

Unlike traditional machinery manufacturing generally using simple features of workpiece as the alignment reference, optical manufacturing, which prioritizes shape tolerances of the machining surface over position tolerances between workpiece geometry features, chooses the machining surface itself as the alignment reference. Thus, the manual alignment of workpiece in optical manufacturing could be very time-consuming when the machining surface is aspheric. Workpiece localization technology is able to automate the workpiece alignment and improve its efficiency. However, there are no relevant reports about application of this technology in the field of optical manufacturing. In this work, the workpiece localization problem for aspheric surface in magnetorheological finishing (MRF) is investigated from aspects of measurement and algorithm. The probe radius error is compensated by applying the polynomial fitting method. A new localization algorithm is proposed in order to improve the computational efficiency for the localization of aspheric surface. Simulation and experiment results verify the validity of the proposed methods. The accurate and efficient workpiece localization in MRF has been achieved and applied in real application which proves its practicability. [ABSTRACT FROM AUTHOR]

Abstract: Stitching test of large optical flats is still quite challenging. In this paper, aiming to reduce the 2nd order error accumulation effect, separation of the reference surface error from the subaperture measurements is proposed in stitching of large flats. The reference error is decomposed into power and astigmatism, residual Zernike polynomial surface and high frequency component, which are estimated or calibrated, respectively. The error separation procedure is then incorporated into the subaperture stitching algorithm. Finally experiments are presented to show the effect of error reductions in stitching test of a 600mm-aperture flat, with reference surface separated and verified by the factory report of the transmission flat. [Copyright &y& Elsevier]

Abstract: In an ion-beam figuring (IBF) process, the desired material removal, which is specified to the contour algorithm to calculate dwell time, decides the calculated process time and the resulted residual surface figure error. Usually, an IBF process with more removal consumes a longer process time, although the resulted residual error is smaller, whereas an IBF process with less removal needs only a shorter process time, but the resulted residual error is greater. Therefore, in order to balance the process time and the residual error, an optimum removal should be determined. In this study, the characteristic relationship between the process time and the residual error on different specified removals is investigated first. The investigation shows that for smaller removals, the residual error decreases rapidly while the process time increases slowly, and for larger removals, the process time increases rapidly without much decrease in residual error. This characteristic makes the figure-prediction curve (process times vs. rediual errors (RMS)) often in the shape of the letter “L”. Therefore, the optimum removal can be determined at the corner of the curve. Finaly, experiments are performed to verify the proposed method. [Copyright &y& Elsevier]

With the development of optoelectronic information technology, high-performance optical systems require an increasingly higher surface accuracy of optical mirrors. The fast tool servo (FTS) based on the piezoelectric actuator is widely used in the compensation machining of high-precision optical mirrors. However, with the low natural frequency of mechanical structures, hysteresis of the piezoelectric actuators, and phase delay of the control systems, conventional FTS systems face problems such as a low working frequency and a large tracking error. This study presents a method for the design of a high-performance FTS system. First, a flexure hinge servo turret with a high natural frequency was designed through multi-objective optimization and finite element simulations. Subsequently, a composite control algorithm was proposed, targeting the problems of hysteresis and phase delay. The modified Prandtl–Ishlinskii inverse hysteresis model was used to overcome the hysteresis effect and a zero-phase error tracker was designed to reduce the phase error. The experimental results reveal that the tracking error of the designed FTS system was <10% in the full frequency range (0–1000 Hz). [ABSTRACT FROM AUTHOR]

Abstract: Subaperture stitching interferometry combined with a test plate is attractive for testing large convex aspheres, but the stitching algorithm is challenging because the aberrations induced by misaligned test surface or test plate are coupled with the surface figure. By relating the subaperture configuration to the overlapping deviations through ray trace and coordinate transformation, the subaperture misalignment is optimally recognized and corrected to give a minimal overlapping inconsistency in an iterative way. Allowing for misaligned test plate, we decompose the induced aberrations into three parts which are corrected by the stitching algorithm, removed in the form of the Zernike polynomials and left uncorrected as residuals. Finally we present simulation results of testing a convex aspheric mirror with a computer generated hologram which shows the algorithm successfully retrieves the surface figure with the test mirror or the hologram misaligned. [Copyright &y& Elsevier]