Abstract:To solve the problem of low folding rate and accuracy of the main reflective surface of paraboloid solid surface antenna, according to the motion form of antenna panel, a kind of deployable mechanism of solid surface antenna is designed. The Lagrange dynamic model is established by position vector equation, vector closed projection method and D-H coordinate transformation matrix, and the driving force of the mechanism is solved. The influence of kinematic parameters on the driving force and the antenna’s fundamental frequency and formation in the closed and deployed state are analyzed, and the response surface method is used to analyze the influence of the structural parameters on the fundamental frequency and the sensitivity. The principle prototype is developed, and the deployment function and modal test are carried out. The results show that the driving force in the process of turn is much larger than that of the deployment process, and it can be reduced by reducing input speed, adjusting the position of the spherical hinge and reducing the initial angle. The fundamental frequency of the antenna meets the design requirement, the influence of the support rod size parameters on the fundamental frequency is greater than that of switching link, the size parameter of switching link can be adjusted to increase appropriately the fundamental frequency. The deployable mechanism can realize the antenna's deployment repeatedly, and the measurement results of fundamental frequency are close to the analysis results, the antenna can realize deployment function and has good dynamic performance.

Abstract:To study the effect of grain size on the mechanical properties and deformation mechanism of polycrystalline copper during the nanoindentation process, a large-scale molecular dynamics simulation model of polycrystalline copper is structured by Poisson-Voronoi method and Monte Carlo method. Based on the Hall-Petch relationship of the nanocrystalline copper, the single-crystalline and polycrystalline copper nanoindentation simulation models with different grain size are established. The nanoindentation process with different grain size are simulated by molecular dynamics method, and the nanoindentation force, internal stress and atomic potential energy of the atoms are calculated. Centrally symmetric parameter method is used to analyze the dislocation nucleation and propagation process in the surface and subsurface of the polycrystalline copper. The results show that the indentation force of single-crystalline copper is higher than that of polycrystalline copper, with the decrease of grain size, that of polycrystalline copper continuously decreases due to softening phenomenon. The high internal stress and atomic potential energy under the indenter leads to the defect evolution region under the indenter. The range of horizontal distribution of defects is larger than that of the vertical distribution, and such defects are limited in the grains around the indenter due to grain boundary network. The internal stress and atomic potential energy in polycrystalline copper with smaller grain size is larger than that with higher grain size, and the stress and potential energy in single-crystalline copper are lowest. Hence, during the nanoindentation process of polycrystalline copper, to improve the mechanical properties and deformation mechanism of nanocrystalline materials, it is suggests to adopt the nanocrystalline materials with grain size gradient.

Abstract:To explore the effect of anisotropy and KOH corrosion process on the mechanical properties of monocrystalline silicon flexible rib structure, the morphological changes of indentation-induced cracks with respect to the crystal orientation on the three primary crystal planes were observed by nano-indentation experiments combined with atomic force microscope (AFM). The change rule of elastic modulus, hardness, fracture toughness of monocrystalline silicon on the three primary crystal planes (001), (110) and (111) with respect to crystal orientation was analyzed. Meanwhile, the influence of KOH corrosion process on the surface mechanical properties of (001) crystal plane was investigated as well. The result shows that with the variation of crystal orientation, the elastic modulus on the (001) crystal plane appears the greatest change, while the hardness and fracture toughness have no significant changes. On the (110) crystal plane, both the elastic modulus and fracture toughness show obvious changes, but the hardness possesses no significant change. However, on the (111) crystal plane, the mechanical parameters (including elastic modulus, fracture toughness and hardness) of flexible rib monocrystalline silicon have no obvious anisotropic behaviors. The directions which are sensitive to the crack propagation are determined on the three primary crystal planes of flexible rib monocrystalline silicon. The surface quality of silicon processed by KOH erosion would deteriorate and the exposed surface micro-cracks and defects would result in the decrease of hardness and fracture toughness, which should greatly weaken the actual fracture strength of flexible rib structure.

Abstract:Manipulator docking hardware-in-the-loop(HIL) simulation system with the manipulator as a mathematical model will cause instability due to the high contact stiffness of the docking mechanism. To accurately simulate the docking process, the manipulator is equivalent to a six-dimensional spring mechanism during the docking process and the characteristics of HIL system are analyzed. Using root locus method, the influences of HIL system parameters with a mathematical model and a six-dimensional spring mechanism on the stability are compared. Based on the -20 dB/dec crossing frequency theory, the stability criterion, the 3D root locus method and the simulation analysis, the stability and reproduction accuracy are studied from three important aspects of the parameter configuration relation, the system stability condition and the dynamics frequency simulation ability. The experimental results show that when the contact stiffness of the docking mechanism is high, the HIL simulation system with a mathematical model manipulator is unstable but the HIL simulation system with a spring mechanism manipulator is stable; the analysis results obtained from the three aspects which satisfy the stability and reproduction accuracy are consistent with the experimental results. The effectiveness of changing manipulator from a mathematical model to a six-dimensional spring mechanism is illustrated.

Abstract:Regarding the problem that the bionic suspension pendulum robot can not grasp the target rod reliably in continuous brachiation process, we propose a staged control strategy, which includes an optimization method to maximize potential energy by adjusting the robot arms’ configuration, a swinging motion optimization method, and a big damping switch and grasp method. For each motion stage, we deduce the desired trajectory of the PID controller of each active joint and the smooth switching condition. Simulations of continuous brachiation between bars with different distance are conducted in the ADAMS software and the MATLAB/Simulink software. Then brachiation experiments are conducted by using the BARDAH robot developed by our lab. In the experiments, the initial bar distance is 1 m and the target bar distance is respectively chosen from 0.5m, 0.6 m, 0.7 m and 0.8m. For each target bar distance, three experiments are repeated and the success rate of the total 12 brachiation experiments is 100%, which indicates that our control method can effectively improve the success rate of the robot continuous brachiation motion.

Abstract:It is very difficult for a robotic manipulator to perceive and manipulate small objects directly using 3D visual sensors within its vision range in the scene where big and small targets are co-existed in 3D clutter scene. To solve the problem, a method for hybrid configuration of vision system based on fixed globally Kinect depth camera and fixed in robotic end effector moving camera (eye-in-hand camera) is proposed, in which the fixed globally Kinect depth camera is adopted to perceive and obtain the point clouds of big targets within its vision range, and their poses are recognized and estimated, which is utilized to guide the manipulator to move and arrive at big targets using path planning technology. An eye-in-hand camera is launched to capture the images of small object. In offline phase, the CAD model of a small object is created. A set of 2D view images are captured by a virtual 2D camera which is located at the surface of a sphere whose center is pointed into an object at different pose and radius, and stored in a database of 3D shape template of the object. In online phase, the scene image captured by a real eye-in-hand camera is explored and matched hierarchically one by one in details based on image pyramid to find all the instances matching with object templates and to compute their 2D poses. Initial 3D pose is obtained with respect to camera frame coordinate through a series of transformations. Rough pose is refined based on nonlinear least squares method. Experiments of pose estimation accuracy and industrial clutter objects sorting application are performed with ABB robotic manipulator, Microsoft Kinect V2 sensor and Micro Vision industrial camera. A checkerboard is employed to determine the true pose of the object. The results show that the position and orientation accuracy is 0.48 mm and 0.62°, respectively, and the recognition rate is 98% with average time 1.85 s, which is much higher than those of traditional feature-based and descriptor-based pose estimation methods.

Abstract:To investigate the effects of hydrogen sulfide (H₂S) on the combustion characteristics of methane (CH₄) in atmospheric pressure range, the 0-D and PFR reactors were adopted in CHEMKIN-PRO chemical kinetics software to investigate the effects of H₂S concentration, excess air coefficient, pressure and temperature on CH₄ ignition delay and NO reduction, meanwhile sensitivity analysis was used to reveal the chemical kinetics mechanism. The modeling results showed that the H₂S could promote the formation rate of active groups (H, O, OH, HO₂, HO₂, H₂O₂), so premixed gas ignition delay time was reduced, and the effect was more obvious at low temperature. The premixed gas ignition delay time is decreased with the increase of excess air coefficient and pressure. The H₂S decreases the CH₄ reaction temperature and reductive group CH_i are generated at lower temperature, so the H₂S decreases the temperature of NO reduction by CH₄/H₂S. But the existing of H₂S reduces NO reduction efficiency to a certain extent, and the effect is more remarkable in fuel-rich atmosphere.

Abstract:The influence of time-varying meshing stiffness on the gear bearing considering the fractal characteristics of the tooth surface is studied. Firstly, the profile of gear is described by the fractal theory, and the Weber-Banaschek formula is used to calculate and analyze the influence of different fractal dimension D on the time-varying mesh stiffness, and the stiffness of different fractal dimension D is taken into the gear bearing system with the factors such as the nonlinear oil film force of the sliding bearing, the comprehensive transmission error and the backlash, etc. The influence of stiffness of different fractal dimension D on the dynamic characteristics of the system is analyzed. The dynamic differential equation is solved by Runge-Kutta method. The phase diagrams, the Poincaré diagrams, the time domain diagrams, the bifurcation diagrams and the three-dimensional spectrum diagrams of the response of the system are obtained. The results show that with the increase of fractal dimension D, the fluctuation of time-varying meshing stiffness decreases, and the system tends to more stable periodic motion; Compared with the stiffness of random disturbance, the gear bearing system is more sensitive to the change of gear meshing stiffness considering the fractal characteristics of the tooth surface, and it can better show the change of system response due to the change of tooth profile; With the increase of damping ratio, the system will tend to relatively stable single cycle motion.

Abstract:To retain the inner ambient temperature of the cryogenic wind tunnel, improve test efficiency and build large-scale cryogenic wind tunnel scientifically, this paper discusses the applicability of regular cryogenic insulation methods to cryogenic wind tunnel, summarizes the research status of the small-scale research-oriented cryogenic wind tunnel and analyses the differences among the external insulation, cold box, internal insulation and integration of internal and external insulation. Based on the literature analysis, it can be found that only the internal insulation is appropriate for large-scale production-based cryogenic wind tunnels. On this basis, three key technologies about the internal insulation system of large-scale cryogenic wind tunnel are elaborated, including designing, cryogenic fluid-structure-thermal analyzing and testing. Finally, future work on the design and construction of the internal insulation system of large-scale cryogenic wind tunnel are prospected.

Abstract:To clarify the effects of gas and liquid media on the performance of high-speed hydrodynamic seal, the comparison analysis and experimental research on the sealing performance of two phases were carried out. The numerical analysis models of gas and liquid phases in the end face fluid region of hydrodynamic seal were established. The effects of operating parameters such as rotational speed, pressure difference, groove depth, groove number, groove-dam ratio and end face structure parameters on gas and liquid leakage and opening force of hydrodynamic seal were analyzed. The test device of hydrodynamic seal was developed independently, and the tests of variable speed, pressure difference and seal face wear were carried out. The effects of operating parameters such as speed and pressure difference on gas leakage rate, liquid leakage rate and seal face wear rate were obtained. The results of numerical simulation and experiment show that the opening force and leakage of liquid seal are larger than those of gas seal at the same speed and pressure. Under different structural parameters, the opening forces of gas phase and liquid phase seal have maximum values. The optimal structural parameters are different for the gas and liquid phase seal when the opening forces reach maximum values. The optimum ratio of slot to dam and the number of optimal grooves in liquid phase seal are smaller than that in gas seal. The opening speed of liquid seal is lower than those of gas seal, indicating that liquid dynamic pressure seal is easier to open than gas dynamic pressure seal. Seal face wear is serious at low speed and almost no wear at high speed. Hydrodynamic seals are more suitable for high speed conditions.

Abstract:To solve the technical problem that the surface finish of single crystal germanium lens cannot meet requirements, this paper carries out numerical control high-speed polishing optimization tests on polyurethane and asphalt polishing molds based on the numerical control high-speed polishing technique. According to the Preston theory, the processing efficiency and the surface quality control ability of the two polishing molds were compared and analyzed through continuous optimization of process flow and parameters with the combination of motion trajectory simulation and power spectral density calculation. Experimental results show that both of the polishing molds obtained high surface accuracies. The polyurethane mold had higher processing efficiency, but its ability to control the microstructure of the surface was poor. The surface roughness RMS of the asphalt polishing mold improved nearly 3 nm compared with that of the polyurethane polishing mold. Finally, after optimization, the combination of polyurethane initial polishing and asphalt polishing technique was proposed and verified by experiments.

Abstract:To decrease the machining error of large structural parts, a comprehensive error model considering thermal deformation was established based on thermal characteristics analysis, and the error compensation verification was carried out. The mechanism of thermal deformation caused by the temperature change of the grating scale was analyzed and the nonlinear temperature variation law of the grating scale was studied by heat flux. The geometric error and thermal error of gantry machining center were modeled separately and superimposed to generate a compound error model. A linear model between the thermal deformation and the temperature change of the workpiece and a comprehensive error model considering the thermal deformation were established. The relationship between the compound error and the thermal deformation of workpiece in the machining process was analyzed. The innovative real-time compensation system was applied by the external mechanical origin offset function of the CNC system, and the error compensation of the gantry machining center was realized. The results show that the compound error model has high prediction accuracy when the machine tool error is only considered, but it cannot be applied to the machining process of aerospace structures with large thermal deformation. The comprehensive error model has a good effect on the machining process of large torque arm, which increases machining positioning accuracy by at least 52%.

Abstract:A novel one-dimensional (1-D) convolutional neural network (CNN) was proposed based on the classic model LeNet-5, aiming at problems of high computational complexity and low anti-noise ability toward rotating machinery intelligent diagnosis: (1) It adopts global average pooling layer instead of fully connected layers in the conventional CNNs, which reduces the computational complexity, model parameters and risk of overfitting, (2) It is trained with randomly dropout raw signals for anti-noise purpose and (3) It uses modified 1-D convolutional and pooling filters, which works directly on raw time-domain signals, fusing two stages of fault diagnosis into a single learning body, feature learning by the alternating convolutional and pooling layers while classification by the global average pooling layer. The bearing data and gearbox data are used in experimental verification and the classic models of LeNet-5, BP neural network and SVM are used as comparison. The results show that the adoption of global average pooling layers can reduce the model computation and improve the diagnostic accuracy under low signal-to-noise (SNR) conditions, and the train strategy of randomly dropout input can significantly improve the anti-noise ability of the model. As a result, the proposed model can realize accurate, fast and robust fault diagnosis under noisy environment. At last, the t-SNE visualization analysis is used to validate the feature learning ability of the proposed model.

Abstract:To solve the complex control problems of multiple key quality characteristics of NC machine tools, based on meta-action theory and two-dimensional House of Quality(HOQ), a three-dimensional House of Quality (THOQ) model with the influencing factors dimension, the meta-action units dimension and the key quality characteristics dimension was established. The action layer factors affecting the key quality characteristics were screened by Ant Colony Clustering Algorithm, and combined with Evidence Reasoning Recursive Theory(ERRT), the autocorrelation matrix of the factors, the correlation matrix between the key quality characteristics and the influencing factors of each meta action unit and performance coupling matrix of meta-action units were established. Based on quality control cost constraint and development time constraint, an optimization model with key quality characteristics fluctuation degree as objective function was established, and the optimal value of the influencing factors were obtained, so that the fluctuation value of the key quality characteristics was minimized. Finally, an example was given to optimize the indexing table motion of a NC machine tool, and the rationality and validity of the model were verified by experiments.

Abstract:To further explore the changing temperature field and the failure mechanism of wet friction pairs, four evaluation indexes of mean temperature rise rate, maximum radial temperature difference, radial temperature non-uniformity coefficient and radial temperature deviation coefficient are introduced, and the evaluation system of sliding temperature rise characteristics is established. Then accelerated life tests are designed based on the actual working conditions. According to the variation role of friction coefficient and the maximum radial temperature difference, the different stages of sliding characteristics are divided. Based on the evaluation system, the role of sliding temperature rise characteristics are studied during running-in period, stable period and unstable period. The influence rules of speed, surface pressure and lubrication volume on temperature rise characteristics are analyzed in stable period. Moreover, the failure warning information of wet friction pairs is explored during unstable period. The study shows that, the evaluation system of sliding temperature rise characteristics can be used to evaluate the performance of sliding temperature, and the friction coefficient and the maximum radial temperature difference can be used as the indexes for judging running-in state of friction disc. The effect of surface pressure on temperature rise characteristic is the most significant compared with other factors. The temperature rise rate, the radial temperature difference and the radial heat dissipation difference increase significantly in unstable period.

Abstract:For the existence of defects in material can affect thermal conductivity, we calculate the thermal conductivity of perfect crystalline silicon and exam the effects of two types of point defect of vacancy and interstitial on the thermal conductivity of bulk crystalline silicon by molecular dynamics simulation applying reverse non-equilibrium method. The simulation results demonstrate that for scatter between phonon and defect, the thermal conductivity decreases with the increasing concentration of both types of the point defect and it decreases rapidly at low concentration condition and gradually gets flat with the increasing defect concentration. The loss of temperature sensitivity to thermal conductivity is observed at relative high concentration condition. In terms of thermal resistivity, the relative additional thermal resistivity is proportional to both types of point defect concentration considered. Furthermore, considering the microcosmic aspect, the inverse relationship between the concentration of point defect and the mean free path of scattering interacted by phonon and defect is deduced from this macroscopic proportional relationship. Taking the slope of the proportional relationship as impact factor to judge the extent of point defect effect on thermal resistivity (thermal conductivity), it is found by comparing the impact factor that the effects of both types of point defect on the thermal conductivity reduce with the increasing of temperature, and the interstitial has a rather more decreasing effect on the thermal conductivity than the vacancy.

Abstract:Transmission error, to a certain extent, is one of the most important indexes to evaluate the meshing performance of spiral bevel gears, which directly reflects the transmission meshing characteristics of the Spiral Bevel Gears and is closely related to the shafting structure. This paper mainly studies the positive design calculation method between shaft structure and transmission error, and proposes a numerical calculation method of the spiral bevel gear transmission error considering the influence of shaft deformation based on the common software tool platform. It is compared with the international advanced design software (KIMoS software) of spiral bevel gear to verify the calculation method of the paper. The influence of shaft deformation on the transmission error of aero-engine spiral bevel gears is analyzed aiming at two kinds of design schemes for shaft structures in this paper. The analysis results show that the different forms of support have little effect on the contact force of the tooth surface, but the support form and the deformation of the shaft have a greater impact on the transmission error. Good transmission error curve of spiral bevel gears can be obtained by changing the support structure of the shafting system. Therefore, the work of this paper can provide reference for studying the relationship between shafting structure and transmission error of spiral bevel gear.

Abstract:This paper addresses the scientific problems in bearing accelerated life test, such as lack of multi-stress acceleration model, and not well understanding of failure law. Firstly, the interface micro failure mode and mechanism of fluid lubricated bearing under environment of vacuum, temperature, preload, speed and microgravity are analyzed. Secondly, the micro contact uniform lubrication model considering multi-stress comprehensive working mechanism is derivated and established, and the numerical solution method based on improved Newton Raphson method is proposed. Thirdly, the orthogonal simulation scheme with 5 factors and 5 levels orthogonal table is designed, the bearing failure law in the work of vacuum, temperature, preload, speed and microgravity is simulated and analyzed, and the failure response value of micro contact surface film thickness, pressure peak, friction factor, maximum undersurface stress which changes with the stress level and contact region dimension is obtained. Finally, the multi-stress acceleration model about vacuum, temperature, preload, speed and microgravity based on response surface method has been established, which is verified by a test of actual engineering example.

Abstract:In order to improve the efficiency and safety in high speed obstacle avoidance under emergency of vehicle with mechanical elastic wheel (MEW), a nonlinear eight-degree of freedom (8-DOF) vehicle model for dynamics simulation was built up by Simulink. The parameters of MEW tire model were identified by Matlab genetic algorithm toolbox according to the experimental data of flat-bed test rig. Considering the driving speed, the trajectory deviation, the steering wheel angle and the rollover evaluation index, an 8-DOF driver-vehicle closed loop system was established. The driving speed and steering properties of driver-vehicle model to rollover stability are analyzed. For high speed path tracking and rollover control under emergency obstacle avoidance of vehicle, the speed control driver model is established based on steering control driver model, which utilizes a predictive load transfer ratio (PLTR) as the rollover index and the rollover controller activates only when the potential for rollover is significant, otherwise, acceleration control strategy will be used for minimum time obstacle avoidance when the longitudinal velocity is less than the expected safety velocity. Simulation results show that the proposed control strategy has good accuracy in both path and speed following and has a better stability of rollover under emergency situation.

Abstract:In order to investigate the cavitation phenomenon of the hydraulic cone valve, the magnitude of radial offset was calculated by the fluid mechanic theory and the radial force analysis of the fluid on the valve core. The solid models of the internal flow field were established by UG. The mesh was divided by using ICEM-CFD software. The numerical simulation of the two-phase flow was performed on the cavitation of the flow field inside the cone valve based on FLUENT. The variation on cavitation was obtained under four factors, such as radial offset, half cone angle, opening degree and back pressure. A visible experiment of the cone valve cavitation was built. A high pixel camera was used to capture the cavitation image of each valve position. According to the experiment results, the simulation results were verified. The results show that the radial offset causes the cavitation position accumulated in the valve cavity on the side of the upper cone. In addition, the strength of the cavitation changes slowly with the half cone angle of 45°. At the same time, when the half cone angle is 45°, and the opening degree is 0.4mm, the strength of cavitation is the most obvious. With the increase of the opening degree, the strength of air mass in the cavitation phenomenon gradually weakens. Combined with the flow capacity and cavitation strength, the half cone angle of 45° is suitable for cone valve. Furthermore, the increasing of the opening degree and back pressure in a reasonable range can effectively suppress cavitation.

Abstract:In order to establish a thermal error prediction model with high prediction accuracy and generalization performance, a thermal error pseudo-hysteresis prediction model based on metabolic theory is proposed in this paper. The pseudo-hysteresis effect of machine tool is found by experimental research, and it is assumed that the thermal error is the result of the coupled action of the temperature rise at key points and the thermal error of the previous moment, and the thermal key points of the machine tool and the average lag time in the typical working conditions are solved. The genetic algorithm is used to optimize the structural parameters of the least squares support vector machine (LS-SVM). Based on the principle of metabolism, the thermal error is iteratively solved and the thermal error pseudo-hysteresis prediction model of the machine tool is established. The results of different prediction models show that the correctness of the hypothesis and the prediction accuracy of the pseudo-hysteresis prediction model is higher, the generalization performance is better, and the thermal error of different rotational speeds can be reduced by more than 90%.

Abstract:In view of the influence of uncertainty and fuzziness of product quality in actual disassembly process, especially the common fault of product, on the selection of disassembly sequence, an objective selective disassembly sequence planning approach with fault features of product was proposed. A disassembly hybrid-graph model was constructed to express the constraints of a product and the product fault matrix was constructed by extracting product fault features. The relational degree matrix between the component fault features and the element of disassembly model was derived by the method of expert advices. The influence of the component fault features on the element of disassembly model was determined by the fuzzy trigonometric function to update the disassembly hybrid-graph model, and the disassembly model elements and disassembly information were modified based on the influence and thresholds to generate the fault disassembly hybrid-graph model. Finally, an optimal or suboptimal disassembly sequence scheme is generated by combining a disassembly sequence optimization algorithm. A case study of turbine reducer demonstrated that the proposed method was more practical in the actual disassembly process and could solve the fuzzy effect of product faults on the disassembly process, the feasibility of disassembly sequence scheme as well as the disassembly efficiency were greatly improved, and the blindness of disassembly was reduced effectively, which proved that the proposed method is more effective for solving disassembly sequence planning problem.

Abstract:To improve the aerodynamic performance of airfoil, a biomimetic fin airfoil is proposed. Taking NACA0018 as an example, a fixed biomimetic fin wing is arranged on the airfoil suction surface, and the relative position and length of the fin wing and their effects on the aerodynamic characteristics of the airfoil and the mechanism of the biomimetic fin wing are analyzed. The numerical results show that the fin wing near the front edge has a significant effect on the large separation flow and the fin wing near the trailing edge has a good effect on the moderate flow separation. The relative length has non-linear relationship with the aerodynamic performance, and when the length is too short, the separation layer cannot be effectively segmented, and if it is too long, the fluid above the separation layer is affected. When the tip of the fin wing just touches the edge of the separation layer, the control effect is the best. The aerodynamic performance of the biomimetic fin wing is determined by the relative position and relative length of the fin wing.

Abstract:A built-in prime benefit of Kriging surrogate model resides in its unbiased prediction and the associated confidence intervals, comparisons have been done between the classical DoE methods and Kriging model based sequential design. This latter considers both the design space global exploration and optimum-neighborhood exploitation. A parallel point-adding training strategy and its corresponding convergence criterion were introduced to improve the model precision. The approach had been illustrated with two classical optimization test functions. Results show not only a more accurate model but also a possibility to reduce the number of sampling points. Finally, the training strategy was experimented for the optimal design of a sliding bearing. Friction power loss per unit load capacity was taken as the objective function to be modeled. Two surrogate model based optimizations had been per-formed based on classical DoE such as Orthogonal Latin Hypercube and Kriging sequential strategy respectively. These two optimization results are compared with a previously optimization using Complex-optimization method. Within a limited number of iterations, the Kriging model based training strategy showed the best convergence to the global optimum among those 3 methods.

Abstract:An improved artificial potential field method (APFM) is proposed for the problem that only the end of manipulator can be guided but the angle of each joint cannot be constrained, and it is difficult to escape from local minimum when traditional APFM is used to avoid obstacles for redundant manipulator. A kinematic model of the manipulator is established and the line segment sphere enveloping box model is established for collision detection. Attract potential field of the end and obstacle repulsive potential field are established in Cartesian, and attract potential field of the target angle is established in joint space, and they work together to guide the manipulator. A virtual target angle is solved in joint space and the virtual potential field is established using Gaussian function to deal with the local minimum problem. The simulations and experiments on the 7 DOF redundant manipulator show that the algorithm can constraint joint pose and guide the manipulator escape from local minimum when trapped, and finally complete obstacle avoidance. At the end of the obstacle avoidance, the maximum error of each joint angle is 0.8°, and the average position error and attitude error are 0.010 m and 2.40°, which are smaller than the traditional algorithm respectively. The motion amplitude of each joint in the obstacle avoidance process is smaller than the traditional algorithm. The improved algorithm can guide the manipulator escape from the local minimum and complete the obstacle avoidance, as well as improve the positioning accuracy of each joint and the end at the end of the obstacle avoidance. The study has certain guiding significance for research and application of obstacle avoidance for redundant manipulators.

Abstract:Four mathematical models of oil film pressure, contact force of asperity, axial force of synchronizer ring and cone torque are established by means of average Reynolds equation and asperity friction principle. The coupling number of oil film thickness and speed difference of synchronization is solved by using 4-Runge-Kutta method. The changing rule of oil film thickness, speed difference, viscous torque, asperity friction torque and total torque are analyzed. After verification of the mathematical model of synchronization, the effects of structure factors such as the width of synchronizer ring, radius of synchronizer ring, cone angle and thickness of friction material of synchronizer are studied by the model. The results show that the increase of the width of synchronous ring results in increasing viscous torque and asperity friction torque, decreasing the decline rate of oil film thickness, the response of asperity friction torque is delayed and the synchronization time is increased. With the increase of the radius of synchronous ring, the viscous torque and asperity friction torque increase, the oil film thickness descends and the synchronization time is shortened. When the friction angle increases, the viscous torque increases, the asperity friction torque decreases, the speed difference descends slowly and the synchronization time prolongs. With the increase of friction material thickness, the asperity friction torque and the changing rate of oil film thickness increase correspondingly, but the minimum oil film thickness and the synchronization time decrease.