China Mechanical Engineering

Friction Model of Robot Joints Considering Influences of Temperature

ZHANG Yinan, DING Jianwan

2023, 34(02): 127-134. DOI: 10.3969/j.issn.1004-132X.2023.02.001

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In order to describe the influences of temperature on serial robot joint friction under continuous operations， a joint friction model was proposed considering the influences of temperature. This friction model might describe the effects of joint temperature changes on joint friction without measuring or estimating temperature. Through experiments， the friction torques of the robot joints were measured as the joint operations continuously at different angular velocities， and the data were fitted based on the theoretical model. By comparing the experimental results， the validity of the joint friction model was verified. This model may describe the variation of joint friction torques more accurately under continuous operations.

Error Transfer Path Identification Method of Meta-action Unit Based on DOF Constraints#br#

LI Jian, ZHANG Genbao, RAN Yan, WANG Yongqin

2023, 34(02): 135-141. DOI: 10.3969/j.issn.1004-132X.2023.02.002

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Accurately identifying the error transfor path of the meta-action unit was the premise of error analysis. A new method was proposed to judge the error transmission path of the meta-action units based on the concept of DOF constraints in mechanical systems. Firstly， the DOF constraint requirements of the precision output parts and the initial error transfer path were determined by analyzing the functions and the structures of the meta-action units. Secondly， the constraint properties of the joint surfaces were analyzed， and the DOF constraint properties of the precision output parts were calculated along the error transfer path. The error transfer path was determined by comparing the obtained constraint property with the designed constraint property. Compared with traditional methods， the proposed method improves the efficiency of the analysis and identification of the error transfer paths greatly.

Modeling of Cutting Force in Helical Milling of Titanium Alloys Based on Oblique Cutting Theory

WANG Haiyan, ZHOU Zhitong, WU YeFU Qilin

2023, 34(02): 142-147. DOI: 10.3969/j.issn.1004-132X.2023.02.003

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By analyzing the machining principles of helical milling and calculating the motion vectors in machining processes， an analytical model of cutting force in helical milling processes was established combined with the influences of side edges and bottom edges on cutting forces. The identification method of cutting force coefficient was put forward based on oblique cutting， and the constraint equations of friction angle， shear angle， and shear stress were derived according to the geometric relationships of oblique cutting processes. The experiments for identification of cutting force coefficient and helical milling of titanium alloys were carried out to verify the simulation values. The results show that the errors between the simulated and the experimental cutting forces are small， while the average error is as 9.55%， which verifies the validity of the oblique cutting coefficient identification method and the correctness of the cutting force model.

Design of Multi-link Independent Suspension Systems with Constant Wheel Track

LI Ronghua, YANG Jingshan, ZHENG Yufeng, ZHOU Wei

2023, 34(02): 148-156. DOI: 10.3969/j.issn.1004-132X.2023.02.004

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In order to solve the existed problems of difficulty in motion control for robots such as track width changes and variety range of camber increases when wheeled mobile robots equipped with conventional suspension surmounted obstacles， a novel independent linkage which was made up of parallel crank mechanisms， offset slider crank mechanisms， and oscillating guide bar mechanisms was designed. Dynamics simulations and analyses were carried out in different terrains with the software ADAMS， and the optimal length of each link was determined. Experiments of robot verified the improvement of controllability， landing ability of the wheels， and the accuracy of robot motions on obstacle surmounting.

An Actuating Response Model of Temperature-controlled SMA Actuators

LU Youjun, SONG Di, MIAO Changqing

2023, 34(02): 157-163. DOI: 10.3969/j.issn.1004-132X.2023.02.005

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Based on heat transfer theory and actuating geometric relationship， an execution response model of temperature controlled SMA actuator was proposed. The parameter values affected by temperature in the model were dynamically modified to improve the response accuracy of the driving model. When the side number of the regular polygon section of SMA wire was less than 8， the laws of improving the response speed were analyzed and obtained. Based on the results of theoretical analysis， the actuating response of SMA wire with a diameter of 1.2 mm， a length of 10π mm， an initial central angle of 30° was tested under a current intensity of 6A. By comparing the experimental results with the theoretical model calculation results， the max error of the whole actuating processes（actuating end point）reduces to 1.8 s， and the execution response model may accurately describe the actuating response.

Ultrasonic Recognition and Performance Degradation Model of Electrical Connector Fretting Wear

LUO Yanyan, WANG Yongpeng , SUN Zihang , LIANG Hong

2023, 34(02): 164-171. DOI: 10.3969/j.issn.1004-132X.2023.02.006

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Aiming at the problems that electrical connectors reducing contact performance by fretting wear in vibration environments， an ultrasonic testing method was used to monitor the characteristic values of wear debris between electrical connector contacts during fretting wear， and to study the wear degree of contacts under different vibration conditions and the degradation law of contact performance. The results show that the vibration frequency， vibration acceleration， and fretting times have positive cumulative effects on the debris accumulation and contact resistance fluctuation. When the electrical connector vibrates axially， the debris accumulation effectiveness is the most obvious. The contact resistance and the total amount of wear debris characteristic values show a very high correlation under high vibration frequency and acceleration. The average absolute errors of SSA-BP performance degradation model are less than 5% based on the wear debris characteristic values.

Research on Problem of Feedback Mechanism Clearances of a Digital Hydraulic Cylinder for Shearer Rocker Arms

QI Panguo, LIU Zhengqi, ZHAO Liwei, ZHANG Xingyuan, ZHAO Lijuan

2023, 34(02): 172-184. DOI: 10.3969/j.issn.1004-132X.2023.02.007

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In order to study the influences of feedback mechanism clearances on static errors and closed-loop stability of the hydraulic system of coal winning machine， the interaction mechanism of 4 kinematic pairs and their clearances in feedback processes was analyzed， and a digital hydraulic cylinder model with feedback mechanism clearances was established. By comparing the position relationship between negative inverse frequency curves of clearances and Nyquist curves of the linear parts， it is found that the clearances do not affect the stability of the system. Using the static analysis method， the static error expression caused by each clearances was derived， and the factors and laws affecting the static errors were revealed. The AMESim simulation model of digital hydraulic cylinder was established and simulated. Correctness of the theory and simulation analysis was verified by experiments.

Calculation Method and Software Development of Gear Fatigue Strength under Small Samples Based on Monte-Carlo Simulation

LI Yang, LIU Huaiju, WEI Peitang, MAO Tianyu, CHEN Difa

2023, 34(02): 185-192. DOI: 10.3969/j.issn.1004-132X.2023.02.008

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The Dixon-Mood（D-M）method used in gear fatigue strength evaluation needed a certain amount samples of tests， and the results might contain deviations. Thus an effective estimation method（the CQUboot method）of gear fatigue strength was proposed based on the Monte-Carlo simulation. D-M method and CQUboot method were verified and compared by a large number of bending fatigue strength tests. Compared with the results of 20～22 samples recommended in GB/T 14230—2021 Test Method of Tooth Bending Strength for Gear Load Capacity， while the sample number reduces to 12， the maximum errors of the D-M method are as 15.76%～24.99%， while that of the CQUboot method is as 8.02%～12.98%. With 12.66% as the maximum allowable error of fatigue strength estimation， the D-M method at least needs 10～18 samples， while the CQUboot method only needs 8 samples.

Aero-engine Fault Diagnosis Based on an Enhanced Minimum Entropy Deconvolution

ZHAO Yike, WANG Jiaxu, ZHANG Xin, WU Lei, LIU Zhiwen

2023, 34(02): 193-200. DOI: 10.3969/j.issn.1004-132X.2023.02.009

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To extract weak features of bearing faults， an enhanced minimum entropy deconvolution method was proposed based on unbiased autocorrelation analysis. In iterative solution of filter coefficients for the method， aperiodic components in the filtered signals were suppressed， the enhanced detection of the periodic fault impact features was realized， and the accurate identification of bearing faults was completed. The analysis results of simulated signals show that the enhanced minimum entropy deconvolution may accurately extract the periodic fault impact sequence from the signals with complex interferences. The applications in aero-engine fault diagnosis verify the effectiveness of the method for fault diagnosis of bearings in complex mechanical structures.

Research on Flexible Job-shop Scheduling Problems with Integrated Reinforcement Learning Algorithm

ZHANG Kai, BI Li, JIAO Xiaogang

2023, 34(02): 201-207. DOI: 10.3969/j.issn.1004-132X.2023.02.010

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The flexible job-shop scheduling problems were transformed into a Markov decision process， and an algorithm D5QN integrated with 5 kinds of deep Q-network (DQN) optimizations was proposed. In the constructing of Markov process， a set of features was extracted to describe the states， and 3 sets of actions were designed by composite rules. The rewards were mapped by direct and indirect methods. The proposed algorithm was compared with the algorithms based on rules， meta-heuristic， and other reinforcement learning， which verifies the proposed algorithm may further decrease the calculating time， and have feasibility and effectiveness.

Effects of Milling on Surface Integrity and Fatigue Performance of TC4 Titanium Alloy by SLM

JI Wenbin, DENG Riqing, DAI Shijie, LIU Chuncheng

2023, 34(02): 208-217,225. DOI: 10.3969/j.issn.1004-132X.2023.02.011

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Aiming atthe problems of poor surface quality and low fatigue performance of TC4 titanium alloys by SLM， the influences of the milling processes on the surface integrity and fatigue performance of the additive parts were studied by three-point bending fatigue tests of additive parts before and after milling. The results show that after milling， the surface roughness Ra of the additive parts is reduced from 12.57 μm to 0.32 μm， the surface hardness is increased from 353. 0HV to 434.3HV， fatigue life of additive parts is increased from 48 272 cycles to 155 463 cycles. After milling， the location of fatigue source of additive parts is transferred from the surface and subsurface to the interior of the specimen， and the fatigue fracture mode is changed from quasi-dissolution fracture to ductile fracture. The surface integrity of the milled specimens is greatly improved， the fatigue crack emergence and expansion of surface fatigue cracks are suppressed， and the fatigue performance is significantly improved after milling of the additive parts.

Forming Process Optimization of Wire and Arc Additive Manufactured High-strength Steel ER120S-G

FANG Xuewei, JIANG Xiao, WANG Zhe, WU Xiaokang, HUANG Ke

2023, 34(02): 218-225. DOI: 10.3969/j.issn.1004-132X.2023.02.012

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Aiming at the problems of lap spacing optimization for ER120S-G high-strength steel based on wire and arc additive manufacturing process， the pulsed gas metal arc welding（GMAW-P）processes were adopted to perform Canny edge extraction and Gaussian smoothing filtering for 5 sets of single-layer weld passes， and different functions were selected to fit the single-pass morphology. Conventional lap model and optimized slant-top lap model were compared， and the optimal lap spacing of them was calculated. The results show that， the sine function fits the weld contour best in the GMAW-P process of high-strength steel， and the optimal lap spacing from the optimized slant-top lap model is as 0.66 times of the weld width. Based on the above results， multi-layer multi-pass bulk samples were fabricated， and the surface quality is good and without obvious defects. The bulk mainly contains needle ferrite， granular bainite， and M-A elements. The tensile strength is anisotropic.

Progresses and Applications of Counter-roller Spinning Technology for Metal Thin-walled Cylinders

ZHANG Lijun, YANG Ning, LI Zhishun, TAO Jishao, XU Jiayi, LI Fan, ZHAO Shengdun,

2023, 34(02): 226-237. DOI: 10.3969/j.issn.1004-132X.2023.02.013

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Counter-roller spinning was a key technique for forming large high-strength metal thin-walled cylinders. The latest research progresses of counter-roller spinning technology for metal thin-walled cylinders were summarized from 4 aspects：plastic deformation mechanism， influence and control of forming accuracy， microstructure evolution and defects， and counter-roller spinning equipment. It is pointed out that the difficulty of plastic flow control caused by time-varying nonlinear characteristics is the bottleneck in engineering applicationes of counter-roller spinning technology. The technical difficulties of counter-roller spinning were analyzed， and the development trends were discussed. It is revealed that the multi-source hybrid active power flexible spinning process of counter-rollers is of a reference for solving the precision spinning forming of ultra-high strength and large size metal thin-walled cylinders.

Welding Seam Tracking System for Gas Metal Arc Welding of Container Girders

GAO Jiapeng, HONG Bo, JIA Aiting, LI Xiangwen, QU Yuanyuan

2023, 34(02): 238-244,251. DOI: 10.3969/j.issn.1004-132X.2023.02.014

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In the processes of automatic welding of container girders， the uneven strong reflection on the workpiece surfaces， arc light， splash， and smoke easily led to inaccurate or difficult identification of weld deviations， so a welding seam tracking system for gas metal arc welding of container girders was proposed. Based on a low-cost structured light vision sensor， a highly robust welding seam feature extraction model was established. The linear slope of the laser stripes was used by the model for optimizing the random sampling processes of the random sampling consistency algorithm which achieved stable extraction of weld feature in complex environments. The welding test results on the surface of uneven and strong reflective workpieces show that the average detection errors of the method in the Y and Z directions are as 0.22 mm respectively and 0.19 mm with the welding parameters of 300 A， 29 V， and 1m/min， which achieves stable high precision welding seam tracking.

Surface Quality of Ultra-precision Grinding of Silicon with Fine Diamond Grinding Wheels

WANG Ziguang, LIU Jinxin, YIN Jian, ZHOU Ping, SHA Zhihua, KANG Renke

2023, 34(02): 245-251. DOI: 10.3969/j.issn.1004-132X.2023.02.015

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In order to achieve high quality surfaces of silicon by ultra-precision grinding， the silicon surface quality ground by mesh number of 5000， 8000， and 30 000 fine grain diamond grinding wheels was studied. The silicon surface roughness Ra was calculated by mathematical model， and verified by experiments. The characteristics of the silicon surface morphology were analyzed. The force trend in grinding processes of mesh number of 5000， 8000， and 30 000 wheels was analyzed by changes of spindle current of grinding machine. The results show that the silicon surface roughness Ra after grinding with mesh number of 8000 grinding wheel is less than 10 nm， and the subsurface damage depth is less than 150 nm. The grinding force of 8000 grinding wheel is steady during the grinding processes， the grinding quality is better than that of mesh number of 5000 grinding wheels， and the grinding stability is better than that of mesh number of 30 000 grinding wheels.

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