China Mechanical Engineering

Key Technologies of Design and Performance Improvement of Heavy-duty and High Precision Machining Robot Bodies for Large-scale Components

FENG Fei, YANG Haitao, TANG Lina, DING Han,

2021, 32(19): 2269-2287. DOI: 10.3969/j.issn.1004-132X.2021.19.001

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According to the summary and analysis of the application background and development status of mobile robot machining for the typical large-scale components， the basic performance requirements of large-scale component processing robot bodies such as the large workspace， high rigidity， high precision， heavy-duty， light-weight， high dynamic response and high load-to-weight ratio were proposed. Furthermore， focusing on the basic performance requirements， the optimization design and robot performance improvement method of heavy-duty and high-precision machining robot bodies were demonstrated， from the aspect of the optimization design of robot body configurations and mechanisms， the development of the high-performance dedicated and professional controller and the open source operating system of machining robots， dynamic calibration of kinematic parameters and real-time prediction and dynamic compensation of pose errors， dynamics modeling of rigid-flexible coupling multibody system， as well as the robot dynamics control and active vibration suppression control. And then， the conceptual design of the configurations and mechanisms of the machining robot bodies utilized on the large-scale components was completed. The innovative design and development of the robot bodies for the large-scale component processing robots may provide high-performance and super flexible robot machining system for the typical large-scale components in aerospace and other fields， and help to promote the improvement of key performance of domestic industrial robots.

Modeling and Tests for Magnetically Coupled Piezoelectric Vibration Energy Harvesters Using a Single Magnet

ZHANG Zhonghua, CHAI Junling, KAN Junwu, LIN Shijie, WANG Shuyun, HUANG Leshuai

2021, 32(19): 2288-2293，2304. DOI: 10.3969/j.issn.1004-132X.2021.19.002

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In order to achieve high reliability and broadband vibration energy recovery， a magnetically coupled piezoelectric vibration energy harvester using a single magnet was proposed. The kinetic equation of the energy harvesters was established. The effects of magnet horizontal coupling distance d， vertical coupling distance h and coupling angle α on potential energy were simulated and analyzed using COMSOL. A prototype was designed and made to test the output characteristics. The testing results show that the potential energy curve of the energy harvesters changes from single potential well to double potential well as d decreases， at the same time there is a better condition where d is as 11 mm， which may make the depth of the double potential well moderate and then reduce the natural frequency of the energy harvesters and broaden the effective frequency band. The increase of h has little effect on the effective frequency band. When h≤2 mm， the natural frequency is reduced compared to non-magnetic coupling（NMC）. When only changing α， there is an optimal combination of parameters（d=14 mm， h=6 mm， α=67.5°）to enable the energy harvesters to obtain a lower natural frequency（16 Hz） and a wider effective bandwidth（23.6 Hz）， which is as 6 Hz wider than that of NMC， then the power generation performance of the energy harvesters is improved.

Study on High Cycle Fatigue Criteria under Multi-axial Random Loads of Chassis Parts

DONG Guojiang , ZHANG Meng, WEI Liuwei, ZHANG Yongqiang

2021, 32(19): 2294-2304. DOI: 10.3969/j.issn.1004-132X.2021.19.003

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In order to find out the application method and life prediction pattern of the multi-axial high cycle fatigue criteria under random loads， based on a brand B-class car， the wheel center six component force signals of test field strengthening road were collected， and the dynamics model of the vehicle multi-body was established， and the virtual iteration method was used to obtain the load time of the knuckle and the connecting points of other parts. The finite element model of knuckle was established， and the accuracy of the finite element model was verified by modal simulation and modal test. The stress component time history was extracted for the node with the minimum lifetime value under von Mises stress. Three type critical plane calculation methods of eight high cycle fatigue criteria were studied， and the normal stress amplitude and shear stress amplitude of the critical surfaces were extracted by multi-axis cycle counting， and the equivalent stress amplitudes of different criteria were calculated， and the prediction rules of amplitude distribution and life expectancy were summarized. The results show that for the amplitude distribution and life prediction， the equivalent shear stress amplitude of the Zhang-Yao criterion is large， and the prediction life is as 1.09×105 times， which is more conservative than that of other criteria. The large stress amplitude of McDiarmid criterion only accounts for 3.4%， the predicted life is as 1.25×106 times， significantly higher than that of other criteria， and the prediction life value of improved McDiarmid criterion is significantly reduced. For the calculation cost， the von Mises criterion does not need to extract the critical surface and the multi-axis cycle count， so the applications are the most convenient. Findley criterion extraction critical surface processes require the calculation of normal and shear stress data for all planes， so the calculation cost is highest.

Design and Tests of a Two-way SMA Bending Actuator

LI Jiefeng, PAN Ronghua, YANG Zhongqing

2021, 32(19): 2305-2311，2320. DOI: 10.3969/j.issn.1004-132X.2021.19.004

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In order to solve the contradictions between the large deformation and the loading capability of flexible skins and satisfy the smoothness and fatigue life of flexible skins in morphing wings， a novel two-way SMA bending actuator was presented， where a SMA plate was employed as adriving element. Based on the shape memory effects of SMA and the bending theory of mechanics of materials， the theoretical formulae for designing were deduced through analyzing the mechanical characteristics of deformation processes of the actuators. Then， the methods of heat forming and anti-deformation training were adopted to fabricate the actuators， and the deformation capability of the actuators was tested. The results indicate that the deformation behavior of the two-way SMA bending actuator designed according to the theoretical formulae agrees with the tested ones. With the heating temperature rising， the deflections and the output forces of the actuators gradually increase until reaching the maximum deflection. With the thickness of the spring steel plate increasing， the maximum deflections and the maximum output forces of the actuators gradually decrease and the response speed of deformation under heating is slowed down， but the response of recovery under cooling processes is accelerated. After cyclic motivations， the deformation performance of the actuators maintain stable.

Influences of Grain Sizes on Contact Mechanics Properties of Polycrystalline Coppers

LIN Qiyin, ZHANG Yuhan, HONG Jun, WANG Chen, ZHANG Ningjing,

2021, 32(19): 2312-2320. DOI: 10.3969/j.issn.1004-132X.2021.19.005

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In order to study the influences of the grain sizes on the contact mechanics properties of the materials， the contact and separation processes of the diamond indenter and the copper substrate with different grain sizes were investigated at the atomic scale， where the molecular dynamics method was utilized and the elastoplastic deformations of the polycrystalline copper substrates were considered. The results show that with different grain sizes， the maximum adhesion force during the adhesive contact processes of the polycrystalline coppers remains unchanged basically， and the maximum normal contact force shows a trend of first increasing and then decreasing with the decrease of the grain sizes. Moreover， the nano-hardness and contact stiffness are respectively related to the changes of the plastic energy and elastic energy during the contact processes， and the change of the nano-hardness possesses a negative relation with that of the contact stiffness generally. Finally， based on common neighbor analysis method， a study of the elastoplastic deformation processes of the polycrystalline copper substrates was conducted， and it is found that the number of grain boundaries strongly influences the nano-hardness of materials， and then further affects the contact mechanics properties.

Wheel-grinding Position and Pose Algorithm of Flank Faces of Cutting-breaking Drill Tips

MA Yuhao, LI Yong, JIANG Lei, DING Guofu

2021, 32(19): 2321-2325,2330. DOI: 10.3969/j.issn.1004-132X.2021.19.006

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The structural parameters of flank faces of cutting-breaking drill tip were defined， and three coordinate systems were constructed and corresponding transformation matrices were analyzed. The parametric mathematical models of drill tip edge and flank face were established. The motion modes of the grinding wheel were described by the coordinate transformation matrixes. By means of the kinematics principle， the wheel-grinding position and pose algorithm of flank face of cutting-breaking drill tip was proposed based on the workpiece coordinate system in CNC grinding processes. The corresponding program was developed in VC++ environment， and a series of grinding processes and tests were carried out to verify the effectiveness of the proposed algorithm. The measurement results show that the proposed algorithm may ensure the structure precision of the flank faces of cutting-breaking drill tip， adjust the poses of the grinding wheel flexibly.

New Technology of Error Induced Remodeling and Precision Cancellation for Ultra-precision Worm Gear Pair Machining

PENG Donglin, ZHOU Qiwu, ZHENG Yong, YANG Jisen, ZHANG Tianheng, WANG Yangyang

2021, 32(19): 2326-2330. DOI: 10.3969/j.issn.1004-132X.2021.19.007

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A new technology was proposed for embedding intelligent full micro-computerized transmission error testing instrument（iFMT instrument） into each link of worm gear master hobbing machine in the form of instrument unit, and dynamic detection technology was used through the whole processes of forming precision worm gear pair. Under the real-time monitoring of iFMT instrument， the independent accuracy of each link was improved， especially by inducing the changes of relevant errors to cancel their original errors， thus significantly reducing the requirements for high-end processing equipment and personal special skills. The results show that adaptive characters of worm gear， worm and cutter， testing instruments and auxiliary testing devices， especially testing technology and processing technology， may guarantee that the proposed new technology may be arbitrarily copied， enlarged or transplanted to other similar application fields.

Material Removal Mechanism during UAG of SiC Ceramic with a Brazed Single Abrasive Grain Tool

DING Kai, LI Qilin, LEI Weining, XU Mingzhou, WANG Xu

2021, 32(19): 2331-2339. DOI: 10.3969/j.issn.1004-132X.2021.19.008

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To study the effects of ultrasonic vibrations on the material removal mechanism during grinding of SiC ceramics under different grinding speeds， a brazed single abrasive grain tool was used to conduct comparison tests for UAG and conventional grinding（CG）. In addition， the tests were conducted on the polished surfaces based on the continuous variable grinding depth methods. The results show that the materials for both UAG and CG of SiC both experience the following changing stages， i. e.， plastic removal→brittle-plastic transition→large scale brittle fracture， with increasing grinding depths of the single abrasive grain. Compared to CG， UAG may effectively enlarge the critical depth of brittle-plastic transition for SiC ceramics when grinding speed is as 1 m/s， and may also produce lower tangential grinding forces and specific grinding energies. However， the differences between UAG and CG forthe critical depth of brittle-plastic transition and grinding forces will be gradually weakened with increasing grinding speed.

Surface Contamination State Evaluation for Remanufacturing Cores Based on Influence Laws of Restoring Coating Mechanics Properties

KE Qingdi, JIANG Feng, ZHANG Peng, TIAN Changjun, QIN Xiaozhou

2021, 32(19): 2340-2347,2356. DOI: 10.3969/j.issn.1004-132X.2021.19.009

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Aiming at the problems of surface contamination of remanufacturing cores before restoring and pretreatment processes in remanufacturing engineering， the influences of surface contamination contents on the performances of restoring coatings were presented by pretreating and restoring experiments. Informed by the investigation of surface contamination contents of remanufacturing cores， the effects of surface contamination on the coating performance were discussed. After cladding the coating samples with different surface contamination contents， the microstructures and mechanics properties of coating structures were tested and analyzed. The testing results show that with increasing of contamination， the mechanics properties of the restoring coating structures are rapidly decreasing with nonlinear correlation. Finally， combining with the mechanics experimental results， the mapping function of influence law was constructed. Considering the service performance requirements of remanufacturing restoring coatings， the reasonable threshold interval of surface contamination content may be given， and then the pretreatment processes of remanufacturing cores may be planned reasonably， which provides data and technical basis for remanufacturing engineering practice.

Steady-state Heat Conduction Topology Optimization Design for Periodic Functional Gradient Structures

LI Xinqing, ZHAO Qinghai, ZHANG Hongxin, ZHANG Tiezhu, CHEN Jianliang

2021, 32(19): 2348-2356. DOI: 10.3969/j.issn.1004-132X.2021.19.010

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A topology optimization design method of steady-state heat conduction for functional gradient structures was proposed considering periodic constraints. The periodic functional gradient topology optimization model was established based on the variable density theory of solid isotropic microstructure with penalization（SIMP）. The macroscopic topology optimization was performed with the minimization of dissipation of heat potential capacity for the overall structures as the objective function and the volume fraction as the constraint， and the volume fraction of each preset gradient layer was extracted in the optimal configuration. The dissipation of heat potential capacity for units was redistributed to achieve the gradient layer periodic constraint. The numerical instability was eliminated with the application of sensitivity filtering method based on partial differential equation， and the design variables were iteratively updated by using the method of moving asymptotes. Through 2D and 3D numerical examples， the influences of the number of discrete units and sub-regions on the macro-structures and micro-configurations were analyzed under the global periods and the periodic layered gradient settings. The results show that the proposed method is able to achieve the optimal design of the functional gradient topology with periodic constraints. The clear periodic functional gradient structures may be obtained under different numbers of sub-regions, and the obtained structures have excellent heat dissipation performance.

Experimental Study of Embedded 3D Printing PDMS Materials for Soft Robots

ZHANG Wei, MA Kaiqi, JIN Guoqing,

2021, 32(19): 2357-2366. DOI: 10.3969/j.issn.1004-132X.2021.19.011

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Based on the independently built embedded direct ink writing（DIW） 3D printing system， the embedded 3D printing of a complex internal structure for the soft robots was realized by using PDMS as the printing material in hydrogel. The properties of the PDMS materials were analyzed in detail and the printing processes were simulated to determine the combination of processing para-meters. The experiments of curing stretching contrast， monofilament round wire printing and round tube printing were carried out to determine the optimal combination of printing parameters. Finally， using the optimal parameter combinations， the complex bionic structures， flexible check valves and soft grippers were printed and related experiments were carried out to verify the feasibility of using embedded 3D printing PDSM to manufacture soft robots with complex structures.

Influences of Parameters on Multi-Size Tin Solder Bump Array Printed by Uniform Micro Droplets

GAO Kun, LI Yingxiang, QI Lehua, WU Lang, ZHOU Yi, DOU Yibo, LUO Jun

2021, 32(19): 2367-2373. DOI: 10.3969/j.issn.1004-132X.2021.19.012

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In order to realize the repair of microelectronics circuits in aviation equipment quickly and accurately， a direct printing method was proposed for preparing uniform tin solder bump arrays with multiple bump sizes. Influence factors of the landing accuracy of printed bumps and the high consistency quality were analyzed. Tin solder bump array was direct printed by utilizing a proprietary 3D printing equipment. The testing results show that solder bump arrays are printed with the height standard deviation less than 6 μm and the landing errors less than ±5 μm， respectively. Solder columns stacked by multiple droplets are remelted and reshaped into uniform solder bump arrays with different sizes by the heating and remelting method. After remelting， the height consistency of remelting bumps is improved remarkably， but the number of stacked droplets should be limited. The testing results provide a novel method for rapidly repairing small batch packages and damaged expensive chips in avionics.

Health Status Assessment of Hydraulic Pumps Based on Multi-sensor Information Fusion and Multi-grained Cascade Forest Model

SHAN Zenghai, LI Zhiyuan, ZHANG Xu, HUANG Yixiang, LI Yanming, LIU Chengliang, ZHANG Xuan

2021, 32(19): 2374-2382. DOI: 10.3969/j.issn.1004-132X.2021.19.013

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The health status assessment of hydraulic pumps was of great significance to the operating state monitoring of engineering equipment. The existing methods based on vibration signal analysis had single data source and low reliability， therefore a method was proposed for evaluating the health status of hydraulic pumps based on multi-sensor information fusion and multi-grained cascade forest. The pressure， temperature， flow and other signals of the hydraulic pumps were collected under different working hours through the test system， and the time-domain features of the signals were extracted to form preliminary features. Multiple classifiers were used to obtain the category probability vectors of the preliminary features， and the results were stitched with the important features selected by the random forest model to form the final features， and then the multi-grained cascade forest was used to evaluate the health status.The testing results show that the classification precision of the proposed method may still reach 99.5% when the training ratio is only 5%， which may effectively improve the accuracy of hydraulic pump health assessment.

Analysis of Mechanics Characteristics and Contact Performance for Electrical Contacts under Great Temperature Variation Conditions

XIAO Shihong, ZHANG Jingke, ZHANG Huiyao, ZHOU Shichao, HE Xianyou, YUE Linlin

2021, 32(19): 2383-2389. DOI: 10.3969/j.issn.1004-132X.2021.19.014

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In order to improve the electrical contact performances of crown spring contacts for electric drill pipes under great temperature variation drilling conditions， the mechanics properties and electrical contact performances of the contacts were studied. Based on the static and thermo-mechanics coupling finite element analysis method， the relationships between the deflection of the reed and the contact pressure， the insertion force and the insertion depth of the pin were analyzed. The variation laws of insertion forces， contact pressures and contact areas for contact parts with different assembly gaps were studied under great temperature variation conditions. The results show that the contact pressure increases with the increase of deflection， and the increases decrease accordingly， and the insertion forces first increase and then decrease with the insertion depths and finally stabilize. The temperature rise causes the contact pressures and contact areas of the contacts to decrease， which reduces the electrical contact performance. When the assembly gap is as 0.07 mm≤δ≤0.2 mm， the impacts on the electrical contact performance are small. Considering the contact pressure， contact area and maximum equivalent plastic strain at 150 ℃， the optimal assembly gap of crown spring contact is as 0.07 mm. The research results may provide references for the structural design and optimization of crown spring contacts for electric drill pipes.

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