China Mechanical Engineering

Visual Positioning Strategy of Cylindrical Lens Based on U-Net Network

CHEN Fengjun, LYU Jiyang, HU Tian, LIANG Xiaosheng

2023, 34(05): 505-514. DOI: 10.3969/j.issn.1004-132X.2023.05.001

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Aiming at the problems of low product yield and long production operation time during the plating processes of cylindrical lens positioning, a visual positioning correction strategy of cylindrical lens was studied based on U-Net network. The cylindrical lens plating processes and characteristics were combined in the strategy to develop a cylindrical lens visual plating system. The Blob analysis and template matching were used as the early visual positioning method, and the workpiece point information was obtained through high-precision matching to generate a segmentation diagram to annotate the original map of the acquisition, and the optimal learning rate of the loss values was selected to train the U-Net network to achieve the segmentation and positioning of the actual workpiece. U-Net was compared to high-precision template matching for different models of workpiece positioning. It is found that U-Net may achieve sub-pixel level positioning error relative to high-precision template matching. Practical application results show that the visual positioning accuracy of the cylindrical lens visual plating system has high accuracy and strong product adaptability, and the eccentric pass rate of the product may reach more than 96%, which meets the requirements of industrial plating tasks.

Research on Interaction between Pedestrian and Automated Vehicle

LYU Wei, GUO Fu , LIU Li, ZHANG Zeyu, WANG Tianbo

2023, 34(05): 515-523. DOI: 10.3969/j.issn.1004-132X.2023.05.002

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From the perspective of the pedestrian-vehicle-environment system, the effects of pedestrian safety facility, AVs yielding behavior, approaching direction and eHMI on pedestrian-AV interaction were investigated. Based on a cave automatic virtual environment(CAVE) simulation platform, the Unity 3D software was utilized to design and develop the AVs driving scenario. Thirty-eight volunteers were recruited for the pedestrian-AV interaction experiments. During the experiments, the participants decision time, decision results and subjective experience were recorded and further statistically analyzed with survival analysis. The results indicate that with the presence of an AV in the traffic, pedestrian safety facility, AVs yielding behavior and eHMI may significantly shorten pedestrians decision time, enhance their interactive experience and improve traffic efficiency. However, the influences of pedestrian safety facility on pedestrians crossing decision and behavior exist from the earlier stage of the crossing gap, compared with AVs yielding behavior. Meanwhile, the efficacy and clarity of a light band-based eHMI are somewhat limited for conveying AVs yielding intention.

Design of Reconstruction Closed-chain Walking Platforms and Research on Obstacle-overcoming Strategy

JI Jialu, YAO Yanan, ZHANG Ying, LAN Guorong

2023, 34(05): 524-532，542. DOI: 10.3969/j.issn.1004-132X.2023.05.003

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In order to solve the problems of obstacle climbing efficiency and ride comfort after reconstruction adjustment of the closed-chain walking platforms, a coupling adjusting mechanism with frame rod length and inclination angle parameters was designed based on the Watt-type closed-chain leg mechanism to reduce centroid fluctuation and drive power requirements while maintaining single reconstruction power. The obstacle probability model was established to calculate the obstacle expectation, and the full cycle obstacle climbing strategy was studied under two-parameter reconstruction. Prototype design was carried out, and walking and obstacle-overcoming tests were carried out. The results show that the two-parameter coupling adjustment design may increase the fit degree between the platform and the obstacle contact surfaces and improve the obstacle ride comfort.

Identification of Key Errors for Large-sized Gear Hobbing Machines Based on Tooth Surface Posture-geometric Error Model

LI Meng, WANG Shilong, MA Chi, XIA Changjiu

2023, 34(05): 533-542. DOI: 10.3969/j.issn.1004-132X.2023.05.004

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In order to study the key geometric errors affecting the machining accuracy of the large-sized gear hobbing machines, a method for identifying key geometric errors of the machine tool was proposed based on the tooth surface posture-geometric error model combined with Sobol method. Firstly, based on the theory of homogeneous coordinate transformation, the tool posture-geometric error model was established. By solving the two-parameter envelope equation of gear hobbing, the coordinate values of the contact trace points of the machined tooth surfaces were obtained, and the tooth surface posture-geometric error model was established. Then, considering the randomness and mutual coupling of geometric errors, the Sobol method was used to analyze the sensitivity of the model, and the sensitivity coefficients of geometric errors were calculated to identify the key geometric errors. Finally, the virtual simulation corrections and verification of the key geometric errors were performed. The results show that the proposed method may effectively identify the key error terms of the large-sized gear hobbing machines.

Study on　Pulsed Laser Layer-by-layer Brazing Processes of Diamond with Nickel-Chromium Alloys

LI Shichun, ZHOU Lei, ZHOU Feisi, SUN Zhuo,

2023, 34(05): 543-555，575. DOI: 10.3969/j.issn.1004-132X.2023.05.005

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Based on the advantages of low energy inputs and small thermal influences during pulsed laser processing, which was applied to the brazing processes of diamond abrasive grains to realize the layer-by-layer brazing formation of multi-layer diamond abrasive grains. Through single-pass and single-layer pulsed laser brazing tests, the influences of processing parameters on brazing formation and diamond damage were studied, and better processing parameters were selected for multi-layer brazing tests. The results show that during the pulsed laser brazing processes, the changes of processing parameters mainly affect the brazing formation and diamond damage morphology by changing the peak power density and linear energy density. When the input energy density is insufficient, the brazing bead and the brazing layer are prone to molten balls, diamond accumulation, insufficient fusion, discontinuity, and unevenness; when the input energy density is too large, it is prone to diamond damage, the loss and escape of powder materials and diamond. When the line energy density is in 14~25 J/mm2 and the peak power density is in 5×105~1.5×106 W/cm2, good smoothness and good diamond morphology may be obtained. Under the parameters chosen from the scope of above parameters, the formation of multiple layer structure is realized by layer-by-layer brazing, and a better surface forming morphology and a lower diamond damage morphology are obtained. Bending test results of the multi-layer brazing sample show that the bonding strength between brazing layer and base metal is good, and the brazing layer stripping phenomenon does not appear.

Tests and Simulation of Thermal Insulation Performance for Aerogel-filled Metal Honeycomb Sandwich Structures

WEN Yanzhen, DENG Yunhua, JIA Zhen

2023, 34(05): 556-562. DOI: 10.3969/j.issn.1004-132X.2023.05.006

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Niobium alloy honeycombs were formed by brazing a Nb-based brazing material to a niobium alloy at a temperature of 1300°C and a holding time of 30 min. Heating tests were carried out on the niobium alloy honeycomb and the aerogel-filled niobium alloy honeycomb，and the transient temperatures of the hot and cold surfaces were determined. A finite element model of the metal honeycomb and the aerogel-filled metal honeycomb was developed in general agreement with the actual test conditions, and heat transfer simulations were carried out for the honeycomb with different geometrical parameters, the influences of core lattice wall thickness, core height and core inner diameter on thermal insulation performance were analyzed, and then the heat insulation mechanism of the honeycomb was summarized. The results show that aerogel may effectively improve the thermal insulation performance of honeycomb; the thinner the core lattice wall thickness and the higher the core height, the better the thermal insulation performance of honeycomb; the larger the inner diameter of core when filled with aerogel, the better the thermal insulation performance, and the larger the inner diameter of core when the honeycomb core is empty, the worse the thermal insulation performance.

Hierarchical Path Planning for Mobile Robots Based on Hybrid Map

WU Xing, YANG Junjie, TANG Kai, ZHAI Jingjing, LOU Peihuang

2023, 34(05): 563-575. DOI: 10.3969/j.issn.1004-132X.2023.05.007

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A hierarchical path planning method was proposed based on a hybrid topology-grid-metric map for mobile robots, to deal with the problems of large search space, inefficiency and low success rate of obstacle avoidance for traditional path-planning methods in a partially unknown, complex, large-scene environment. Firstly, the robot operation environments were described as a grid map and divided into several grid sub-maps. The topological framework was obtained by extracting the location relation of the sub-maps as the key nodes, and the local region of grid maps was represented elaborately to construct a hybrid topology-grid-metric map. Then, the robot’s path was planned hierarchically in the different regions of the hybrid map. Floyd algorithm was used to plan the interregional path between sub-regions on the topology map. An improved A* algorithm was proposed to search the intraregional paths of each sub-map for the grid map. The filtering strategy of extension points, the mechanism of bidirectional search, and the elimination technique of redundant waypoints were introduced to improve the efficiency and quality of path planning. And the globally optimized initial path was generated by merging several interregional and intraregional paths. Finally, a dynamic obstacle-avoidance path planning method was proposed based on the deep reinforcement learning framework for the dynamic obstacles in a partly unknown environment on the metric map. In the framework, the mechanism of value-classified experience replay was devised to increase the utilization of experience samples and the efficiency of model training. The experimental results demonstrate that the proposed method has the high path-search efficiency and obstacle-avoidance success rate, and the generated paths are both safe and smooth.

Mirror Milling Machining Path Optimization for Thin-walled Parts Based on Singularity Avoidance

QIAN Long, ZHANG Liqiang, GAO Qiuge, YANG Jie

2023, 34(05): 576-583，594. DOI: 10.3969/j.issn.1004-132X.2023.05.008

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In the double five-axis mirror milling processes, due to the singular problems caused by the sudden change of the rotation axis, the surface processing quality and processing efficiency of thin-walled parts were reduced. Based on the analysis of the causes of the singularity problems, a method was proposed for optimizing the machining paths in the singularity regions. Based on the concept of C-space, under the boundary constraints of the singular areas, the tool axis vector in the mirror milling processes were kept perpendicular to the workpiece surface, and the alternative tool axis vector was determined by the minimum tool axis vector distance, the tool axis vectors in the singular region was locally corrected. Then, B-spline curve fitting was performed on the entire processing path, and an optimization model was established based on the minimum parameter curve strain energy. By adjusting the parameter curve, the smoothness of the path was improved, the processing efficiency was ensured, and the processing quality was improved. Finally, the effectiveness of the proposed method was verified through simulation experiments and actual machining results. The results show that minimum wall thickness error is reduced by 50%, the maximum wall thickness error is reduced by 75%, and the overall wall thickness error range is reduced by 68.75%. At the same time, the complete path processing time is decreased by 2.1%.

Research on Intelligent Tool Fault Diagnosis System of Machine Tools with Cloud-Edge-Device Collaboration

LI Dongyang, YUAN Dongfeng, ZHANG Haixia, ZHENG Anzhu, DI Zijun, LIANG Daojun,

2023, 34(05): 584-594. DOI: 10.3969/j.issn.1004-132X.2023.05.009

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In order to improve the accuracy of tool wearing fault diagnosis, three-axis acceleration sensors were adopted to collect the wearing vibration data of tools. Based on the data analysis, a fault diagnosis algorithm of tools was proposed based on the integration of long short-term memory and multi-scale convolutional neural networks, the multi-scale features in both spatial and temporal domains were captured, the accurate recognition of tool wearing status was realized. Meanwhile, a cloud-edge-device collaboration architecture applicable to tool fault diagnosis was designed to achieve the timely warning of tool faults by efficient collaboration among the bottom production lines, edge servers and the cloud industrial internet platform. The results show that the proposed system may accurately identify the tool faults and reduce the maximum completion time delay of fault diagnosis tasks.

Bio-inspired Design and Research on Light Ductile Soft Grippers

GUO Zhonghua, JI Chenghao, DOU Mengyu, WANG Xue

2023, 34(05): 595-602，609. DOI: 10.3969/j.issn.1004-132X.2023.05.010

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In order to make grippers soft with good load capacity, inspired from the structure of the herbaceous plant stem and corolla, a spiral envelope gripper was designed similar to the corolla folding with rigidity enhancement scheme as the plant stem. Each claw actuator was spiral-curved, and the stiffener panel was embedded in each claw structure chamber to improve the output forces, with little influence on the deformation angle. The soft actuator also possessed lower hysteresis with stiffener panels. The soft gripper was fabricated, assembled and tested. The testing results show that the soft gripper is light with small closing volume, good unfolding，enveloping and load capacity were obtained, which had good gripping effectiveness for axisymmetric objects, and effective for objects that may not be manipulated by traditional grippers such as non-axisymmetric objects, except for the corolla folding motions, and the gripper may around objects to enhance gripping effectiveness.

Structural Design of Full-automatic Pathological Staining System Based on FISH Technology

LIN Chengxu, GAN Lang, TAN Xinping, LI Xuemei, YAN Wang, LI Qian, CHEN Gang, LIAO Guanglan, LIU Zhiyong

2023, 34(05): 603-609. DOI: 10.3969/j.issn.1004-132X.2023.05.011

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FISH technology was a common method to detect the nucleic acid sequence of malignant tumor cells. It was widely used in the field of cancer diagnoses and treatments. In order to realize the full automation of FISH experiments, a full-automatic pathological staining system was designed, which was provided with multi axis control arm, reagent sampler, slide, cover slide fixture, auxiliary module and so on. The positioning erorrs of the multi axis control arm are less than ±0.1 mm, the accuracy of extracting and discarding the pipette head is more than 99.5%, the success rate of extracting the cover glass is more than 99%, and the erorrs of micro reagent sampling are less than 0.6 μL. The errors of adding a large amount of reagent are less than 0.5 mL, the temperature control erorrs of slide clamp are less than ±1 ℃, and there is no reagent leakage. The results of biological experiments show that the system has good fluorescence staining effectiveness, the signal points are clearly visible, and the interpretable rate of fluorescence image is more than 90%.

Fast and Accurate Estimation Method of Forklift Loads Based on Improved Kalman Filter

HUANG Zexiong, LIU Lan, HUANG Yunbao, LI Haiyan, HUANG Donghua

2023, 34(05): 610-622. DOI: 10.3969/j.issn.1004-132X.2023.05.012

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Aiming at the demands of real time, fast and accurate load estimation for telescopic handlers with harsh working environment and complex operating conditions, the mathematical model and the solution algorithm for the load estimation of telescopic handlers were studied. Firstly, three load estimation schemes were proposed and analyzed by using various sensors assembled in the existing functional modules of telescopic handlers. After comprehensively comparing the advantages and disadvantages of each scheme, the mathematical model of load estimation was determined and established based on dynamics principle. Then, the loads were taken as the state variable of the estimated system, the real time signals such as the pressure of the hydraulic system, the luffing angle of the boom and the telescopic length of the telescopic boom were taken as the measured values, the load calculation formula established based on the dynamic rotation law was taken as the observation processes between the state variable and the measured values, and the Kalman filter algorithm was used to solve the mathematical model. At the same time, in order to solve the problem that the state variables changed in the recursive processes of Kalman filter algorithm and a large number of new measurement data lost the ability to correct the state variables, a load estimation algorithm was proposed based on improved Kalman filter. Finally, the offline tests and online tests of a super long load telescopic handler with different loads were carried out. The results show that the maximum absolute error of the estimation results is less than 91 kg for 454 kg light load, and the average absolute percentage error is less than 3% for 1100 kg, 2268 kg, 3368 kg and 4536 kg heavy loads. The response time of the stable estimation value may be within 1 s, which is completely better than the actual application requirements. And this method has simple model and strong portability, and may be extended to the online load estimation of cranes, grabbers and other construction machinery.

Analysis and Experimental Research for Leaking Behavior of Labyrinth Seals under Gas-liquid Two-phase Conditions

CAO Hengchao, XU Yiren, SUN Nannan, LU Jian, ZHU Guixiang, LI Yongjian

2023, 34(05): 623-629. DOI: 10.3969/j.issn.1004-132X.2023.05.013

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In order to solve the problems of lubricant oil leakage at the shaft end of crankcase on large marine diesel engines, the leakage behavior of labyrinth seals under gas-liquid two-phase conditions was studied by numerical simulation and experiments. In order to reveal the sealing mechanism and leakage law of labyrinth seals in gas-liquid two-phase environments, the flow field in labyrinth seals was calculated by using FLUENT, and the DPM was used to analyze the escape behavior of oil droplets. The sealing structure and the working conditions were built based on a test rig, and the oil leakage rate was measured under different rotating speeds, the functions of different structural features of the shaft end seals were studied, and finally two effective improvement measures were given. The results show that the staggered labyrinth structure may significantly reduce the air leakage compared with the straight labyrinth. The outward transport on liquid phase by air are greatly weaken by adding staggered labyrinth. In addition, the oil leakage may be significantly reduced by appropriately using labyrinth structure to return oil.

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