According to the design theory for parallel mechanism based on positions and orientation characteristics (POC), a new 3-DOF PM with reconfigurable moving platform RPa3R-R+RSS, was proposed． Firstly, the output characteristics of the PM were analyzed, which show that the moving platform may produce n-translation and 1-rotation (nT1R, n=2,3) and has partial motion decoupling. The PM may produce a specific rotational output motion around one of three specific axes x, y, z by reconfigurable architecture of the moving platform. The degree of freedom and the coupling degree of the PM were calculated. Secondly, a general kinematics model of the PM for a configuration of arbitrary rotational shaft of the moving platform was established according to the kinematic molding principles based on the ordered single-open-chain（SOC） units. Lastly, the kinematics of the output configuration of moving platform with rotating around the z axis were analyzed, including the positive and inverse position solutions, workspace, rotation capability, singularity conditions, and the calculation and simulation of velocity and acceleration.
According to the structure and movement characteristics of five-axis automatic drilling and riveting systems, the off-line programming system architecture of automatic drilling and riveting was constructed, and the motion simulation module was developed. Firstly, considering that the characteristics of all points were relatively fixed in bracket coordinate system, an inverse kinematics solution was proposed based on the moving coordinate system’s point positions. Based on this, a real-time interference detection route planing algorithm was proposed.Then, motion simulations were realized in DMU module of CATIA by CAA secondary development method. Lastly, an example of aircraft panel part was given to demonstrate the feasibility of this system. The results indicate that it may effectively identify interference parts and avoid interference by inserting viaing points.
The structures and storage characteristics of a cantilever rack stereoscopic warehouse was analyzed, a multi-objective mathematical model was built based on the maximization of the utilization rate of the stereoscopic warehouses and the stability optimization of the cantilever rack stereoscopic warehouses, and intelligent algorithm was used to optimize analyses. Finally, through the simulation, the results show that the algorithm is effective, and the multiple population genetic algorithm is proved more suitable than simple genetic algorithm in solving the storage position optimization for cantilever rack stereoscopic warehouses.
Most tractors used two motors to control, and led to high energy consumption, large heat release and complex control. Due to these problems, an electropermanent magnet sucker was designed to provide enough normal forces between wheels and the pipe walls. So, the tractor might be drived by only one motor. The finite element method was used to simulate the electropermanent magnet suckers, which analyzed the impacts of various size parameters on the magnetization and demagnetization performances. Based on the simulation results, a group of reasonable size parameters was selected. The errors between the actual values and the simulated values are less than 15% by the experiments of the electropermanent magnet sucker, and the well tractor with electropermanent magnet sucker may drag over 3 000N.
For the purposes of providing guidance for optimization of hydraulic control systems and energy saving control methods for forging manipulators, the model of energy flow and calculation model of energy for forging manipulators were extended, and the control characteristics and energy dissipation characteristics of forging manipulator hydraulic systems were analyzed under stretching processes. The distribution laws of energy dissipation in hydraulic systems were found out, and the key points of low energy efficiency were analyzed. The results show that the energy dissipation characteristics of the forging manipulator hydraulic systems have following features. The energy transfer efficiency of clamp lifting and rotation may be higher than 60%. The energy transfer efficiency of walking motion of cart is only 17%. When the clamp drops, the gravitational potential energy is almost converted to the throttling losses of the lift control valves. If single system pressure driving mode does not match different loads of multi actuator reasonably, there will be huge throttling losses.
A method of rescheduling mode selection was proposed to solve the problems of disturbance cumulative rescheduling scheme selection based on data learning. The cumulative disturbance time was used to quantify the implicit disturbance, and the real-time production and processing status were reflected by data. The cumulative disturbance rescheduling model was constructed, and the factors and decision labels of rescheduling decision were obtained based on genetic simulation. The characteristics of the simulation samples were analyzed, and based on the data feature reduction mapping, the SVM-based classification decision model was constructed to learn the internal relationship between the production situation and the rescheduling mode, which would help the production managers to make the decision quickly and improve the response speed. Finally, the rationality and effectiveness of the rescheduling selection framework were verified by experiments.
Nano materials were widely used because of their unique structures and properties,and nano joining technology was also developed.In the field of nanofabrication，although there were many varieties of advanced microscopy methods,it was difficult to observe and analyze many phenomenons and behaviors of nano materials by experiments due to the restrictions of real-time observation.Molecular dynamics simulation within nanometer spatial scales and nanoseconds time scale allowed insight into molecular motions on an atomic scale since it was consistent with the time and spatial scales of many processes in nanofabrication.Therefore,it was feasible to use molecular dynamics simulation to simulate the properties of nanomaterials and the dynamic behavior of atoms in the nano joining processes. Herein,the progresses of molecular dynamics simulation of nano-scale materials,including nanomultilayers,nanowires,carbon nanotubes and nanoparticles in the nanojoining processes,as well as applications of these materials for joining of large size materials were reviewed. Meanwhile it is illustrated that the simulation results are in good agreement with the experimental ones.The existing problems,possible solutions and development trends were discussed.
A lane detection algorithm was proposed based on projection and hyperbolic fitting. Firstly, the collected images were preprocessed, and the feature points of lane marks were extracted by the informations such as the widths of lane lines. Secondly, the vanishing points were located according to the positions and the direction angles of feature points, lanes of near field were extracted based on the vanishing points, and then supplemented the lane. Finally, lanes of near field information and hyperbolic fitting were used to find the best lanes where there were a crooked road. The experimental results show that the algorithm proposed herein may effectively detect the lanes with different curvatures, and the proposed lane detection method has high accuracy rate. The algorithm exhibits high robustness under various environments.
To solve the problems of the deviation of slings and the deficiency of vertical force caused by non plumb-bob effects of slings in the experiments of perimeter truss deployable reflectors in space orbit, a gravity compensation method was proposed herein with active horizontal positioning and moving slings. Firstly, the relationships between the horizontal displacement of truss nodes and truss deployment angles were obtained by kinematic analyses of the deployment processes, so that the positions of the truss nodes could be followed in deployment processes accurately. Furthermore, static mechanics analyses of the deployment processes were carried out to determine the masses of counterweights. Finally, the rationality and correctness of the proposed method were verified by comparing with the hanging wire counterweight method based on ADAMS.
A belt safety monitoring method was proposed based on vision, and a visual monitoring system for belt tearing was constructed. Aiming at the image degradation from interference during operations of belt conveyor, Wiener filtering method was used to restore the degraded images. In order to recognize the belt cracks with high-speed moving in real time, CamShift algorithm was used to track and capture the targets of fast-moving sequence images of belt cracks. Canny operator was used to extract the edges of belt cracks, and the detected edges of belt cracks were expented outwards by adding a value δ, increasing the weights of the detected cracks, and more robust edge detection results were obtained. Finally, belt crack prediction model was constructed based on SVM, geometric characteristics, such as pixel area and length width ratio of the belt crack images were taken as the model inputs to predict belt crack states. Experimental results show the effectiveness of the method of belt tearing detection method proposed herein.
An optimization model of electromagnetic driven system of bladder power pump was built based on the theory of electromagnet design and optimization theory.The optimal structure design parameters were obtained by SQP method.According to these parameters,3D models of the electromagnetic driven systems and bladder power pumps were established.The electromagnetic driven performance,the temperature rise performance and the micturition performance were simulated by using ANSYS Workbench.The simulation and experimental results show that the optimization model and 3D finite element(FE) models are effective and practical. Comparing with the formers, the volume of electromagnet is reduced by 65.45%,the weight of electromagnet is reduced by 60.25%,the electromagnetic driven force is increased by 2.09%,the maximum of intravesical pressure is increased by 2.74%,the maximum of urine flow rate is increased by 14.22%,the temperature rise is increased 1.64 ℃.The results improve the micturition performance.The research may provide theoretical and technical guidance for the design of portable,reliable and suitable for animal and clinical studies of the bladder power pumps.
Aiming at the disadvantages of high impact, large mass and poor dynamic characteristics of impact cylinder UAV ejection system, a bionic pneumatic muscle driven UAV ejection system was proposed. By the method of utilizing the small nonlinearity of pneumatic tendons and configuring the wedge angles, the project may ameliorate the stress conditions of the UAVs and slow down the acceleration fluctuation. The mathematical modeling and dynamic analysis of the ejection system were carried out, and the Simulink model was built to emulate the system. Combing the MATLAB and Simulink, the existing acceleration trajectories were further optimized by multi-objective genetic algorithm. The optimized acceleration track may improve the acceleration mean, the energy utilization rate of the pneumatic muscle and the take-off speed. At the same time, the acceleration peak values are reduced, and the acceleration fluctuations are reduced by 76.79% on the original basis. Simulation and optimization results show that the system may avoid the disadvantages of impact cylinder ejection system, and make the acceleration changes smoothly and reduce the maximum overload of the whole systems.
Considering the vibration problems of parallel stabilized platforms in heavy loading, a 3-UPS/S parallel stabilized platform driven by hydraulic servo was studied. Based on the principles of virtual work, the dynamics model of the stabilized platform was established. Considering the actual working conditions, the dynamics model was simplified to obtain the vibration model of the stable platform. In order to improve the reliability of the calculation, experiments were carried out to obtain the actual stiffness of a single branch. Based on this, the stabilized platform modal tests were carried out by using pulse excitation method, the correctness of the vibration model was verified by comparing the measured values and theoretical values of natural frequencies. Finally, the influences of hydraulic cylinder vibrations on the movement of the moving platform and vibration responses of moving platform were analyzed under no-load and load. According to the analyses and calculations, the poor stability of the mechanisms is mainly caused by the vibrations of the hydraulic cylinders and the forced vibrations of the moving platforms under heavy loads.
A new method for fault diagnosis of bearings was presented based on K-SVD and HBW-OOMP. Firstly,K-SVD dictionary training algorithm was utilized to construct a redundant dictionary containing impulsive components and the disadvantages of less adaptability of fixed structure dictionary were overcome. Then, HBW-OOMP algorithm was employed in selecting the best atom and solving the sparse coefficients. The signals were decomposed adaptively with the maximum principle of the envelop spectrum kurtosis. The fault features were extracted by the proposed method from simulated and experimental signals respectively. The results show that the method may achieve the extraction of impulsive components from strong noise, which demonstrates the effectiveness and practicability.
The uncertainties of design parameters were not considered in the existing milling process parameter optimization methods, resulting in the optimization results difficult to meet the performance requirements of the actual products. The reliability-based design optimization method was used to determine the optimal milling process parameters. In the proposed method, the surface roughness was the objective function, and the reliability that the maximum milling force less than the given value was taken as the constraint. Considering the variations of milling speeds and feeds per tooth, a reliability optimization model of milling process parameters was established, Kriging approximation and radial basis function approximation were used to replace the implicit relationships of milling surface roughness, milling force and design variables. Finally, Monte Carlo simulation-sequential approximation programming was used to solve the optimal design of the proposed model. The reliability optimization results were verified through milling experiments. The results show that this method may effectively reduce the milling surface roughness and ensure the reliability requirements of the maximum milling force.
For the flexible job shop-scheduling problem with AGVs, a hybrid genetic algorithm was proposed based on the time window and Dijkstra algorithm. Firstly, a mathematical model of the dual resource scheduling of AGV/machine was established. Secondly, three solutions were used to deal with conflicts and collisions in multiple AGV path planning. Then in order to take integrated scheduling of machine and AGVs into account, three encoding chain structures and the crossover and mutation operators of AGV coding chain were designed. Meanwhile, the Dijkstra algorithm was combined with the time window principles in the decoding operations of genetic algorithm, which may accurately plan a shortest path without collisions and conflicts for the taskes of AGVs. Finally, the feasibility, effectiveness and superiority of this algorithm were verified by numerical examples.
With the development of tailor-made automotive panels,a new flexible punching system was proposed for personalization punching of automotive panels based on 6-axis industrial robots.Meanwhile,in order to get accurate and non-interference punching trajectory,the interactive tool path generation method was proposed in 2D planes based on shape features of punching pliers.This system is highly flexible and can be adjusted easily to punch all kinds of holes in different positions.
A novel 3-UPU parallel mechanism was proposed，which has 2R1T degrees of freedom （DOFs）.Based on the geometric properties of the uniparted hyperboloid，the mechanism's symmetry about middle plane was discovered，and the non instantaneity of the mechanism's DOF was approved.It was verified by simulation that the moving platform might rotate continuously around any axis in the middle plane.The inverse kinematics solutions were derived by a new method of solving the attitude matrix of platform with two rotational DOFs，and the workspace was analysed.The research results provide theoretical references for the applications of the mechanisms.
The various defect morphologies were impacted on wheel rollers by pendulum machine. The rolling contact fatigue damage characteristics of the normal and two kinds of defected wheel materials were investigated using an improved MMS-2A rolling-sliding wear testing machine. The residual stress distributions on wheel materials after impacting were simulated by ABAQUS, and the crack initiations and propagating mechanism were discussed. The results indicate that the residual tensile stress vertical to the wheel tread emerges on subsurface materials, contributes to the crack initiation and growth compared with the normal wheels. The length and angle of cracks around ball defects are both larger than that around ballast defects under the same impact energy conditions. Moreover, the crack surfaces of the subsurface cracks at the edge of the around ball defects are wider and extend internally along the 45° expansion angle.
The applications, evaluations and fundings of projects at Mechanical Engineering Discipline (Division Ⅱ of Engineering Sciences) of the National Natural Science Foundation of China(NSFC) in 2018, as well as the research progresses of undertaking programs and the achievements of finished programs, were reviewed. Typical innovative achievements during project execution were summarized. Specific measures and corresponding effects of Mechanical Engineering Discipline were stated, such as academic exchange and cooperation, talent cultivation, and academic team construction.