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RB-SiC ceramic is one of the most important and useful material as optical precision elements in many scientific research fields. In this paper, a novel cold atmospheric plasma (CAP), which is based on the precision grinding process in surface technology to modify at room temperature (RT) for grinding with a combination of plasma oxidation surface modification is proposed. To identify the performance of the proposed cold atmospheric plasma (CAP) method on the surface modification of RB-SiC ceramic, precision grinding test was conducted. To reveal the fundamental issue in the grinding of RB-SiC ceramic, numerical calculation and model analysis were conducted to investigate the effect of the composite process on grinding forces and the mechanism of subsurface material removal in the presence of plasma oxidation. As a result of the method included the kept constant during the precision grinding of the composite process self-adaption-grinding process to avoid the deviation caused by second grinding particle entry. As a summary, we provides a significant cold atmospheric plasma-precision grinding compound process toward the establishment of the basic theory by analyzing the mechanism of the simulated design and computation. The process and technical difficulties of RB-SiC ceramic and mechanism of subsurface material removal during precision grinding were be solved.

YAG wafers are the most host laser crystals used for high-power lasers, which are usually machined by grinding to meet the required accuracy for laser components. Warping deformation induced by the residual stress is one of the main damages for YAG wafers after the grinding process, which will seriously decrease the service accuracy and life of the lasers. Developing theoretical model of warping deformation is of great significance to achieving the ultra-precision machining of YAG wafers. The cutting depth of single abrasive and grinding force in self-rotating grinding were investigated by considering the kinematic trajectory of abrasives, brittle-to-ductile transition, elastic mechanics, elastic deformation of the grinding wheel and strain rate effect. A theoretical model of warping deformation in self-rotating grinding of YAG wafers was developed based on the cutting depth and grinding force. The influence of subsurface damage and residual stress on warping deformation was analyzed based on the theoretical model and finite element simulation. Self-rotating grinding tests of YAG wafers were performed, and the results showed that the warping deformation decreased as the wheel rotational speed increased, and increased as the abrasive size, workpiece rotational speed and feed speed increased. The experimental results agreed well with the simulated results of the theoretical model, indicating that the theoretical model can accurately predict the warping deformation induced by self-rotating grinding process. This work will not only enhance the understanding of the essence of the wafer warping induced by ultra-precision machining, but also provide a guide for optimizing the processing parameters in self-rotating grinding of YAG wafers.

The CFD method is capable to investigate the influence of the geometrical parameters of the air film and the manufacturing error on the performance of aerostatic bearings. To facilitate the CFD based design of the aerostatic bearings, a parametric GUI for analyzing the performance of aerostatic bearing is developed, by which the performance of aerostatic bearings with varying geometrical parameters and manufacturing errors can be simulated efficiently. Furthermore, as a case study, the influence of the key geometrical parameters and the manufacturing errors on the performance of rectangular aerostatic bearings is investigated, which provides guidance for the design and manufacturing process of an aerostatic stage. Finally, the experimental test was conducted to verify the simulation result.

A novel BiOCl/CAU-17 2D/2D heterostructure composite was prepared by in situ growth of ultrathin BiOCl nanosheets on the surface of CAU-17 nanorods, and showed admirable photocatalytic activity and favorable stability.

Micro-rod YAG single crystals are the most commonly used laser crystals for laser gain mediums with a high power. However, brittle fracture and crack damages are easy to occur in the grinding process of micro-rod brittle crystals due to their large length-to-diameter ratio, high brittleness and high hardness. In this work, the modal, frequency and harmonic response of the transducer under ultrasonic elliptical vibration are analyzed by using finite element simulation. Then, the mechanical structure of ultrasonic elliptical vibration system was designed and optimized based on the ultrasonic elliptical vibration theory and finite element simulation. To verify the reliability of the transducer, ultrasonic vibration experiments were are carried out to measure the resonance frequency, amplitude and impedance characteristics of the transducer. The vibration synthesis experiments under different phase differences and different voltages were performed to verify the rationality of the structural design of the ultrasonic elliptical vibration system. An experimental platform of ultrasonic elliptical vibration assisted centerless grinding was developed, and UEVCG tests of micro-rod YAG crystals were performed. The influences of voltage, phase difference and pallet angle on surface roughness, PV value and cylindricity of the micro-rod YAG crystals were systematically analyzed. The ultrasonic elliptical vibration parameters were optimized based on the range analysis results of the orthogonal test. The results indicated that ultrasonic elliptical vibration effectively improved the surface quality and cylindricity of the micro-rod YAG crystals compared with traditional grinding. This work will not only enhance the understanding of the ultrasonic elliptical vibration principle, but also provide a technical support for precision and high-efficiency machining of micro-rod brittle materials.

To solve the problem of fast convergence in large aperture plane optics continuous polishing, the concept of vibration-assisted polishing is proposed in this paper. The paper first builds a low-frequency short-range vibration processing platform based on large-size polishing tools. Then, the kinematics and polishing pressure of the optics without vibration and vibration are analyzed. Furthermore, the pressure distribution under the element is simulated based on the finite element method. Finally, the material removal rate (MRR) is calculated based on Preston equation, which proves that the removal rate of optics under vibration condition is higher. In this paper, the problem of optics removal efficiency in continuous polishing is solved and the material enhanced removal mechanism is revealed.

The AUV (Autonomous Underwater Vehicle) navigation process relies on the interaction of a variety of sensors. The side-scan sonar can collect underwater images and obtain semantic underwater environment information after processing, which will help improve the ability of AUV autonomous navigation. However, there is no practical method to utilize the semantic information of side scan sonar image. A new convolutional neural network model is proposed to solve this problem in this paper. The model is a standard codec structure, which extracts multi-channel features from the input image and then fuses them to reduce parameters and strengthen the weight of feature channels. Then, a larger convolution kernel is used to extract the features of large-scale sonar images more effectively. Finally, a parallel compensation link with a small-scale convolution kernel is added and spliced with features extracted from a large convolution kernel in the decoding part to obtain features of different scales. We use this model to conduct experiments on self-collected sonar data sets, which were uploaded on github. The experimental results show that ACC and MIoU reach 0.87 and 0.71, better than other classical small-order semantic segmentation networks. Furthermore, the 347.52 g FOLP and the number of parameters around 13 m also ensure the computing speed and portability of the network. The result can extract the semantic information of the side-scan sonar image and assist with AUV autonomous navigation and mapping.

Laser crystals of rare-earth oxide are primary host materials for making solid-state lasers of large power. However, brittle fractures and cracks are easily formed on the crystal’s surface and subsurface during abrasive machining process owing to their high hardness and brittleness, which will seriously reduce output power of the lasers. In this work, a grinding coolant was synthesized through dispersing GO nanosheets in water, and the grinding experiment of GGG laser crystals assisted by GO coolant lubrication was systematically performed. The plastic deformation mechanism of GGG crystals induced by GO assisted grinding was revealed at close-to-atomic scale by Raman spectrum and cross-section TEM detection technologies. The results indicated that the plastic deformation of GGG crystals during GO assisted grinding was affected by the interlayer slip and filling actions of GO, and was dominated by polycrystallization nanocrystals and amorphous transformation caused by the crystal plane slipping. The use of the GO coolant enabled to lower friction at the abrasive-substrate interface significantly owing to their self-lubricating effect, thus resulting in improved ground surface quality, in comparison with conventional grinding. This work will provide a new theoretical basis and technical support for high-efficiency and low-damage ultra-precision grinding of laser crystals.

During the nanoparticle colloid jet polishing process to obtain ultra-smooth surface, cavitation is easy to occur because of the intense fluid turbulence. Cavitation interacts with nanoparticles in the colloid solution, which has a great influence on the processing quality of the ultra-smooth surface. In this paper, the collision between nanoparticles and ultra-smooth surfaces under the micro-jet effect formed by cavitation is studied. Molecular dynamics simulation result shows that the collision of nanoparticles changes the atomic position of the collision region of workpiece, resulting in lattice distortion, coordination number and atomic potential energy increased. The ultrasonic cavitation system is used to prepare the monocrystalline silicon workpiece that effected by nanoparticle colloid cavitation. After the process, the dark spots could be observed on the surface of workpiece by SEM. The dark spots are the traces of the collision between the nanoparticle and workpiece, which verify the molecular dynamics simulation results. XPS detection of the surface of monocrystalline silicon workpiece processed by nanoparticle colloid cavitation has been done and the result is slightly different from the workpiece that have not been processed by cavitation. The difference illustrates that the chemical bonding between nanoparticles and monocrystalline silicon surfaces has formed. The simulation and experimental results show that the cavitation is beneficial to the removal of the material of the workpiece by nanoparticles, but it has an adverse effect on the formation of ultra-smooth surface.

Continuous polishing (CP) using a pitch lap plays a vital role in finishing large flat optical workpiece. The effects of key mechanical parameters in CP can be characterized by the contact pressure and friction force at the workpiece/lap interface. In this study, a novel on-line interfacial contact pressure and friction force wireless measurement system is developed for the practical CP process. These mechanical factors varying with polishing time are measured in experiments and its effect on material removal is theoretically analyzed. A liquid bridge model is proposed to explain the negative contact pressure at slurry channel edge and the enhanced contact pressure at the abrasive slurry lubrication condition. Experimental results reveal the material removal coefficient is linear to time average COF under given polishing conditions and there exists significant non-uniformity in material removal coefficient along the workpiece radial direction.

Full aperture continuous polishing using pitch lap is a key process of finishing large flat optical workpiece. The friction force of the workpiece and pitch lap interface significantly affects material removal. In this work, the friction force was determined by a measurement system that uses force transducers to support the workpiece. Experimental and theoretical analyses have been carried out to investigate the evolution of friction force with polishing time and its effect on material removal. Our results show that the friction coefficient of the workpiece/lap interface decreases during polishing, which is due to surface smoothing of the viscoelastic pitch lap by loading conditioner. In addition, the spatial average and uniformity of material removal rate (removal coefficient) increases with the increase of friction coefficient, which is due to rough lap surface, provides more sharp asperities to charge the polishing particles.

Full-aperture polishing is one of the most important processes in fabricating large flat optical elements. Control of the elements’ surface figure to a high precision in a determined manner has been a major challenge in this process. This study focuses on the converging mechanism and deterministic control of the surface figure in the full-aperture polishing process. A novel balance equation for material removal is proposed to correlate the primary aspects of the polishing condition to the surface figure. The removal balance equation reveals that the final surface figure is determined by the spatial distributions of three factors, including the relative velocity, polishing pressure, and removal coefficient. The dependence of these factors’ distribution on the polishing condition is detailed in theory and experiments, and systematic methods to deterministically control these factors’ distribution are proposed. This study is a significant attempt to reveal the converging mechanism of the surface figure and develop a deterministic full-aperture polishing process.

A 2D/2D BiOIO

Path planning obtains the trajectory from one point to another with the robot's kinematics model and environment understanding. However, as the localization uncertainty through the odometry sensors is inevitably affected, the position of the moving path will deviate further and further compared to the original path, which leads to path drift in GPS denied environments. This article proposes a novel path planning algorithm based on Dijkstra to address such issues. By combining statistical characteristics of localization error caused by dead-reckoning, the replanned path with minimum cumulative error is generated with uniforming distribution in the searching space. The simulation verifies the effectiveness of the proposed algorithm. In a real scenario with measurement noise, the results of the proposed algorithm effectively reduce cumulative error compared to the results of the conventional planning algorithm.

Nanoindentation and nanoscratch tests of YAG single crystals were systematically performed. The mechanical properties including elastic recovery rate, elastic modulus, nano hardness and fracture toughness of YAG single crystals were obtained by the nanoindentation tests. The surface morphologies of the scratched grooves were analysed using scanning electron microscopy. The formation characteristics of YAG single crystals induced by varied-depth nanoscratch indicated that there was distinct brittle-to-ductile transition phenomenon during the scratching process. Surface radial cracks occurred prior to the edge-breaking phenomenon, and transverse cracks extending to the surface of the work material dominated the brittle removal of YAG single crystals. A theoretical model of the edge-breaking size during the nanoscratch process was developed by considering the stress intensity factor, elastic recovery rate, and residual force. This model indicated that the edge-breaking size increased as the normal force, average elastic recovery rate and elastic modulus increased, but decreased as the nanoindenter tip radius, fracture toughness and nano hardness increased. When the average elastic recovery rate was within 17.5%–20% (the maximum elastic recovery rate was within 35%–40%), the values predicted by the theoretical model agreed well with the experimental values, and the average error was less than 5%. The model could provide theoretical guidance for analysing the surface generation characteristics of brittle solid materials during the abrasive processing at brittle removal regime.

This paper presents an effective framework for correspondence field estimation. The core idea is to construct pixel-level and superpixel-level patch matching to achieve high accuracy estimation as well as fast speed computation. To this end, a hybrid edge-preserving supported weighting approach is first developed, which contributes to better performance on the pixel level, especially on those in the regions of fine structures. Then, a local Minimum Spanning Tree (MST) is constructed to describe regions and develop the adaptive smooth penalty weights, so that the over-patching in large textureless regions can be effectively avoided. In addition, the MST is further extended to handle occlusions in way of edge preserving strategy. Finally, all the above treatments are collected into an optimization model where the objective function is developed in terms of Markov Random Filed (MRF). In computation, a fast yet efficient iterative optimization strategy is developed. Our approach achieves favorable place on optical flow benchmark, which locates at the top two and top four for endpoint error and angular error evaluations among more than 130 approaches listed in the webpage.

The key challenge for multiple vessel cooperative localization is considered as data association, in which state-of-the-art approaches adopt a divide-and-conquer strategy to acquire measurement-to-target association. However, traditional approaches suffer both the computational time and accuracy issues. Here, an improved algorithm under Random Finite Set statistics (RFSs) is proposed, in which the Probability Hypothesis Density (PHD) filter is utilized to address the aforementioned issues, by jointly estimating both the number of vessels and the corresponding states in complex environments. Furthermore, to avoid the prior requirement constrain with respect to the PHD filter, the pattern recognition method is simultaneously utilized to calculate the birth intensities. Simulation results exhibit the proposed approach performs better than normal PHD for multiple vessel cooperative localization, in scenarios of unknown birth intensity.

Thermal assistance is considered a potentially effective approach to improve the machinability of hard and brittle materials. Understanding the material removal and friction behaviour influenced by deliberately introduced heat is crucial to obtain a high-quality machined surface. This paper aims to reveal the material removal and friction behaviours of RB-SiC ceramics scratched by a Vickers indenter at elevated temperatures. The material-removal mode, scratching hardness, critical depth of the ductile–brittle transition, scratching force, and friction are discussed under different penetration depths. The size effect of scratching hardness is used to assess the plastic deformation at elevated temperatures. A modified model is established to predict the critical depth at elevated temperatures by considering the changes in mechanical properties. The results reveal that the material deformation and adhesive behaviour enhanced the ductile-regime material removal and the coefficient of friction at elevated temperatures.

Free-form surfaces have been widely used in complex optical devices to improve the functional performance of imaging and illumination quality and reduce sizes. Ultra-precision grinding is a kind of ultra-precision machining technology for fabricating free-form surfaces with high form accuracy and good surface finish. However, the complexity and variation of curvature of the free-form surface impose a lot of challenges to make the process more predictable. Tool path as a critical factor directly determines the form error and surface quality in ultra-precision grinding of free-form surfaces. In conventional tool path planning, the constant angle method is widely used in machining free-form surfaces, which resulted in non-uniform scallop-height and degraded surface quality of the machined surfaces. In this paper, a theoretical scallop-height model is developed to relate the residual height and diverse curvature radius. Hence, a novel tool-path generation method is developed to achieve uniform scallop-height in ultra-precision grinding of free-form surfaces. Moreover, the iterative closest-point matching method, which is a well-known algorithm to register two surfaces, is exploited to make the two surfaces match closely through rotation and translation. The deviation of corresponding points between the theoretical and the measured surfaces is determined. Hence, an optimized tool-path generator is developed that is experimentally verified through a series of grinding experiments conducted on annular sinusoidal surface and single sinusoidal surface, which allows the realization of the achievement of uniform scallop-height in ultra-precision grinding of free-form surfaces.

Constant- and varied-depth nanoscratching tests of GGG single crystal were carried out at different scratching velocities. The morphologies of the scratched grooves and chips were analysed using scanning electron microscope. The experimental results indicated that higher scratching velocity led to shallower penetration depth, shallower residual depth, and larger continuous chips. Increasing the scratching velocity could effectively improve the plasticity and reduce the brittle-to-ductile transition depth of GGG single crystal. Based on the contact stress and contact area between the analysed sample and Berkovich indenter, a model for predicting the penetration depth was developed, which took into account the strain rate effect and elastic recovery of materials. The model was verified using constant- and varied-depth nanoscratching tests, and the predicted and experimental results were in good agreement. Subsurface damage underneath the ductile surface was characterised using transmission electron microscope. The TEM results demonstrated that higher scratching velocity led to the slipping planes appearing in more directions, which prevented the generation of long slipping plane and reduced the depth of the damage layers. The plastic deformation of GGG at the scratching velocity of 100 μm/s was dominated by poly-crystalline nanocrystallites and amorphous phases, and was similar to that at the low scratching velocity. This study provided a fundamental understanding of the strain-rate dependence of surface/subsurface deformation mechanisms of GGG during ultra-precision machining.

YAG single crystals are the primary host materials for solid-state lasers at multi-kW scale and must be processed using ultra-precision grinding to achieve a satisfactory dimensional precision and surface integrity. However, the deformation mechanism of YAG crystals is not well understood, which has thus hindered the development of high efficiency grinding technology for the crystals. In this work, precision grinding of YAG single crystals was investigated. Ductile-like surfaces that are free of cracks and brittle-ductile surfaces that consist of fractured spots and ductile striations were found after grinding. The deformation mechanisms associated with the two types of surfaces were explored with the aid of transmission electron microscopy (TEM). The results indicated that the deformation involved in the formation of the ductile-like surface was mainly caused by the slippage of (0 0 1) crystal planes, along with the formation of dislocations and stacking faults and the distortion of atomic planes. The brittle-ductile surfaces were generated by the plastic deformation due to the formation of nanocrystals and nanovoids, combined with brittle fracture caused by the crack propagation initiated at intersections of slip lines. A theoretical model was developed to predict the grinding force in the ductile-like grinding process, which has taken the combined effect of strain rate, random distribution of abrasive radii and elastic-to-plastic transition depth into account for the first time. The key model parameters were obtained using a genetic algorithm trained using the experimental force data. The modelled force agrees well with the measured. This model enabled an in-depth understanding of the deformation mechanism of a crystal solid involved in ultraprecision grinding and the effect of strain rate on its material removal.

Polycrystalline materials like Cu–Pb alloy consist of four types of microstructural components, including grain cells, grain boundaries, triple junctions and vertex points, the mechanical propertie...

Scene flow is an essential part of a stereo-based perception system for autonomous driving and mobile robotics. As in most of these platforms, the computing resource is limited but the computing requirement is high, embedded and parallelized algorithms are of vital importance for real-time tasks. This paper develops a cross-platform embedded scene flow algorithm by using an OpenCL (Open Computing Language) programming. Meanwhile, we propose a method to achieve a good performance by using a novel coarse-grained software pipeline for the embedded stream application. Experimental results show that the proposed algorithm can boost the average processing speed to 50 fps for different commercial off-the-shelf (COTS) hardware, including desktop graphics processing units (GPUs), field-programmable gate arrays (FPGAs), and mobile phone platforms. For certain GPUs, the peak frame rates can also reach 1000 fps. By comparing the efficiency among the serial platform, we illustrate that with the help of OpenCL programming, COTS platforms can provide enough computing resources for the stereo-based perception algorithm.

Cutting tools may heat up during use, causing them to deform. Such an effect degrades the surface microstructure of potassium dihydrogen phosphate (KDP) crystals via ultra-precision fly cutting. In this process, thermal expansion of the tool displaces the tool tip perpendicular to the workpiece processing surface. Such displacement is difficult to measure experimentally due to the limited sensitivity of displacement sensors and the severe conditions present during cutting processes. In this study, a cutting surface simulation model based on machine kinematics of the fly cutting and a thermal model based on the experimental results of the principal cutting forces are established in KDP crystal ultra-precision flying cutting to explore the specific impact on the workpiece due to the thermal deformation of the tool. The relationships between cutting parameters and principal cutting forces are thereby determined. The relationships between tip heat inflow, tip displacement perpendicular to the workpiece processing surface, and crystal surface microstructure were simulated. The results demonstrate that the heat deformation of the tool slightly influences the roughness and waviness of KDP crystal surfaces, and increases their surface slope, thus influencing surface precision. This directly affects the optical performance of such crystals.

The spindle rotation error is one of the important factors that affect the precision of the machined parts. The study of spindle rotation error is of great significance for finding the source of error, predicting the surface shape error of machining parts and improving the machining accuracy of ultra-precision machine tools. The structural of the aerostatic spindle this article focuses on is motorized spindle and the spindle tilt error has the maximum effect on the machining precision. A new method for measuring the rotation error of ultra-precision aerostatic spindle based on interference fringes is proposed in this paper. By using the principle of phase shifting interferometry, the mathematical model between the shape of interference fringes and the motion law of the spindle rotor is established by theoretical modeling. The interference fringes are processed with gray, smooth filtering, expansion corrosion, and edge detection and so on. The distance and direction of the interference fringes are calculated in the coordinate system, so as to get the spindle tilt error. Finally, the measurement system for the spindle rotation error of the aerostatic spindle is developed. The accuracy and effectiveness of this method are shown based on the experimental results.

To get insight into nano-scale deformation behavior and material removal mechanism of RB-SiC ceramic, nanoscratch experiments were performed using a Berkovich indenter. Structure changes in chips and subsurface deformation were characterized by means of Raman spectroscopy. The result shows that the SiC phase underwent amorphization in ductile chips, while no amorphous feature can be observed in brittle chips and substrate within scratch groove. The following estimated stress surround the indenter reveals that amorphous deformation in ductile chips is governed by tangential stress (above 95 GPa), whereas the dislocations-based substrate deformation mechanism was dominated by normal stress. In the end, the effects of normal load and scratching velocity on the scratch behavior including scratch residual depth, elastic recovery and friction coefficient that related to RB-SiC ceramic deformation mechanism were also analyzed. With the increase of normal load, the deformation mechanism transfers from ductile to brittle fracture mode and cause the decrease of elastic recovery and the increase of residual depth and friction coefficient. Furthermore, the increased high density of dislocations as a result of the increased scratching velocity give rise to the increase of scratch hardness, which finally result in the increase of elastic recovery and decrease of residual depth and friction coefficients. This study contributes a new understanding of the brittle material deformation mechanism during a nano-scale scratching process.

To understand the anisotropy dependence of the damage evolution and material removal during the machining process of MgF2 single crystals, nanoscratch tests of MgF2 single crystals with different crystal planes and directions were systematically performed, and surface morphologies of the scratched grooves under different conditions were analyzed. The experimental results indicated that anisotropy considerably affected the damage evolution in the machining process of MgF2 single crystals. A stress field model induced by the scratch was developed by considering the anisotropy, which indicated that during the loading process, median cracks induced by the tensile stress initiated and propagated at the front of the indenter. Lateral cracks induced by tensile stress initiated and propagated on the subsurface during the unloading process. In addition, surface radial cracks induced by the tensile stress were easily generated during the unloading process. The stress change led to the deflection of the propagation direction of lateral cracks. Therefore, the lateral cracks propagated to the workpiece surface, resulting in brittle removal in the form of chunk chips. The plastic deformation parameter indicated that the more the slip systems were activated, the more easily the plastic deformation occurred. The cleavage fracture parameter indicated that the cracks propagated along the activated cleavage planes, and the brittle chunk removal was owing to the subsurface cleavage cracks propagating to the crystal surface. Under the same processing parameters, the scratch of the (001) crystal plane along the [100] crystal-orientation was found to be the most conducive to achieving plastic machining of MgF2 single crystals. The theoretical results agreed well with the experimental results, which will not only enhance the understanding of the anisotropy dependence of the damage evolution and removal process during the machining of MgF2 crystals, but also provide a theoretical foundation for achieving the high-efficiency and low-damage processing of anisotropic single crystals.

Underwater sensing and detection still rely heavily on acoustic equipment, known as sonar. As an imaging sonar, side-scan sonar can present a specific underwater situation in images, so the application scenario is comprehensive. However, the definition of side scan sonar is low; many objects are in the picture, and the scale is enormous. Therefore, the traditional image segmentation method is not practical. In addition, data acquisition is challenging, and the sample size is insufficient. To solve these problems, we design a semantic segmentation model of side-scan sonar images based on a convolutional neural network, which is used to realize the semantic segmentation of side-scan sonar images with few training samples. The model uses a large convolution kernel to extract large-scale features, adds a parallel channel using a small convolution kernel to obtain multi-scale features, and uses SE-block to focus on the weight of different channels. Finally, we verify the effect of the model on the self-collected side-scan sonar dataset. Experimental results show that, compared with the traditional lightweight semantic segmentation network, the model’s performance is improved, and the number of parameters is relatively small, which is easy to transplant to AUV.

The crystallographic orientation and voltage dependence of nanopattern morphology and size of electropolished Al has been revealed and established. However, the reported models failed to explain these experimental results. Here we developed an improved model that explicitly includes the calculated anisotropic interfacial energy of clean Al/ethanol interface for the perchloric acid-ethanol based solution with high volume percentage of ethanol. The model predicts existing regions of six types of nanopattern morphologies based on the Turing pattern bifurcation criterion, and reasonably explains experimental results. These findings help gain deeper insights into the nanopattern formation mechanism of electropolished Al and other metals.

With the development of the modern state of optical engineering, large diameter (400×400 mm) of optical element processing and its whole surface shape accuracy is 0.1 micron (λ/ 6). It's on special crystal material single point diamond fly knife cutting ultra-precision machine tools put forward higher request, the bed is equipped with stable, the lathe bed equipment for the foundation design, and set the parts of the material. We think about the precision analysis of the external influencing factors of equipment, and design the model of equipment bed. In the bed model, the static simulation analysis is made under the two schemes of basic design and optimized reinforcement, respectively. And we compared the necessary design model and optimized design model. The total deformation was 0.409 microns for bed base, 0.268 microns for oblique rib, and 0.312 microns for circular rib. And we analyzed the deformation in X, Y and Z directions.

Path planning plays a significant role in robot navigation applications, as path exploration ability requires the knowledge of both the kinematics and the environments. Most of the current methods consider the planning process alone instead of combining the planning results with tracking control, which leads to a significant reduction in the availability of the path, especially in complex scenarios with missing GPS and low positioning sensor accuracy. This paper proposes a reinforcement learning-based path planning algorithm, which aims to consider the errors caused by the robot’s motion during the dead-reckoning process and effectively reduces the cumulative error within the optimization process. The simulation conclusion in the 2D scene verifies the effectiveness of the algorithm for reducing the cumulative error.

This paper presents a Simultaneous Localization And Mapping (SLAM) algorithm in the underwater environment. In this paper, forward-looking sonar is used to extract environmental features to establish a 2D grid map. The SLAM algorithm estimates the AUV’s (Autonomous Underwater Vehicle) pose by fusing multi-sensor data, including IMU data and the DVL data. To verify the algorithm, we simulated the experimental environment using the UUV-Simulator software. The results show that the algorithm can effectively suppress divergence and accurately locate the AUV.

In this paper, mechanical properties of RB-SiC ceramics, such as hardness, elastic modulus and fracture toughness, are characterized through indentation technique using a Vickers indenter at elevated temperatures ranging from room temperature to1200 °C realized by laser heating. The indentation size effect, load-displacement curves and relationship between crack length and applied load are studied in order to determine hardness, elastic modulus and fracture toughness accurately. The results show that the Meyer’s index and Vickers hardness decrease with the increase temperature. It indicates that the permanent plastic deformation of RB-SiC ceramics is mainly responsible for the indentation size effect and the reduction of hardness at elevated temperature. Both material softening and plastic deformation will contribute to the indentation creep at elevated temperature as shown in the load-displacement curves. The elastic modulus decreases with the increase of temperature due to increase of contact depth as a result of less elastic recovery. In the indentation test for calculating fracture toughness, only radial-median cracks are identified by the relationship between crack length and applied load at all temperatures, although the fracture mode observed at the indent corner changes from transgranular at room temperature to intergranular at elevated temperature. As more energy is consumed by intergranular facture and cracking-healing takes place due to oxidation, only short crack length appears in the indentation test which implies an increase of fracture toughness with the increase of temperature. However, this tendency has an exception at the highest temperature of 1200 °C. This is because the free Si softening in RB-SiC specimen fails to resist crack propagation at extremely high temperature. Consequently, the crack length increases again which leads to the increase of the calculating fracture toughness at the highest temperature. These variations of hardness, elastic modulus and fracture toughness with temperatures will account for the possible change of material removal regimes occurred in some thermal-involved hybrid machining of RB-SiC ceramics.

Continuous polishing is the first choice for machining optical elements with a large aperture. The lubrication in the continuous polishing is an important factor affecting the surface quality of the optical elements. In this study, the lubrication system between the optic element and polishing lap was analyzed firstly and then was verified by the measurement experiment of the friction coefficient. In addition, the numerical simulation model of the mixture lubrication was established. The polishing pressure distribution and material removal distribution can be obtained by the model. The influences of the rotating speed, optical element load, and surface roughness of the polishing lap on polishing pressure were also analyzed. Finally, the influence rules of the lubrication on the surface shape of optical elements were revealed by the polishing experiments.

The crystallographic orientation dependence of nanopattern morphology and size of electropolished Al at a fixed voltage (40 V) has been revealed and established. However, systematic experimental studies, with samples’ crystallographic orientation exactly determined, on the effects of voltage on nanopattern morphology and size has been largely lacking. Here, miscut monocrystalline Al samples are electropolished in a common electrolyte at voltages 20–60 V. Various nanopatterns (pits, pits plus stripes, stripes, dots) with distinct morphologies emerge with increasing voltage. The findings that morphologies transform gradually with misorientation angle were explained from the perspective of surface structure sensitivity. Nanopattern sizes remain largely constant with misorientation angles but increase with voltages till about 40 V, level off and decrease at higher voltage. A reported model was reexamined to explain the observed voltage dependence of nanopattern size by considering the overlooked effects of voltage on dissolution and adsorption. These findings reveal the voltage and crystallographic orientation dependence of nanopattern morphology and size, and provide critical data for theoretical investigation into the nanopattern formation mechanism of electropolished Al.

Gallium nitride single crystal (GaN) is difficult to achieve high-efficiency and low-damage machining due to anisotropy, high hardness and brittleness. Nanoscratch tests of GaN single crystals was conducted on (0001) plane along different zone axes, and the anisotropy dependence of material removal and deformation behaviors were investigated systematically. The results showed that crack-free plastic deformation of GaN crystals could be acquired along different zone axes, which was dominated by phase transition, polycrystalline nanocrystals, amorphous transition, as well as close-to-atomic scale damages including stacking faults, dislocations and lattice distortions. As the stress increases, special surface radial cracks with the same orientations caused by shear stress will appear on the groove surface, and striated and step-shaped brittle fractures can be induced by the propagation and intersection of the cracks. The processing along [11–20] zone axis was more conducive to achieve the plastic removal and deformation, deeper penetration depth and less phase transformation. The higher stress along [1-100] zone axis induced more phase transition from hexagonal system to cubic system. This work will enhance the understanding of the anisotropy dependence of material removal and damage mechanisms, and provide a guide for achieving high-efficiency and low-damage machining of GaN crystals.

Nanoscratch tests of LuO single crystal under different scratch velocities were performed using Berkovich and spherical indenters. The experimental results indicated that shallower penetration depth and lager continuous chips were generated during the scratching process when a higher scratch velocity was used. Moreover, two types of plastic flow lines were formed on the crystal surface after testing. A theoretical model on the penetration depth of scratching LuO single crystal was developed by considering the elastic recovery and strain rate effect. The predicted results were found to agree well with the experimental results, and the deviation was within 10%. The transmission electron microscopy (TEM) analysis results of the crack-free subsurface generated during the nanoscratch tests revealed that the ductile removal mechanism dominated by nanocrystalline and amorphous phases. Pressure-induced defects, such as dislocations, stacking faults, and nano twins were observed inside the nanocrystalline phase. High-angle annular dark-field (HAADF) images of the subsurface indicated that a higher scratch velocity could effectively reduce the subsurface damage depth when the normal force was maintained constant.

In order to solve the online clean maintenance problem of the optical frequency-doubling crystal module in the final optics assembly, a crystal loop case is developed for better controlling the clean maintenance process. The study presents a detailed research on the cleanliness of the crystal loop case during the online maintenance process and the installation sequence of the crystal modules in the crystal. It first established a fluid simulation model of the crystal loop case system according to the online maintenance process and then analyzed the isolation effect of inlet velocity on the polluted air in view of the cleaning effect of the crystal loop case. Based on the simulation principle of gas–solid two-phase flow and the tracking results of the solid particle contamination, the range of air inflow is given for achieving the best cleaning status of the loop case. The optimal sequence of crystal module is explicit for its installation in the crystal loop case of frequency-doubling crystal module. The experimental setup has been built to examine the cleaning state of the crystal loop case, and the simulation result has been validated. The research on the cleanliness of crystal loop case can provide a useful reference for the ultra-clean manufacturing of line replaceable units and the closed loop control of cleaning in high-power laser facility.