最新刊期
卷 47 ， 期 12 ， 2023
- 摘要：Gears are the most widely used transmission parts in the modern mechanical transmission system. The precision and surface quality of gear tooth profiles have great influence on the precision, smoothness, reliability and noise of gear transmission. The machining process of gears usually goes through the process of initial cutting, heat treatment, initial grinding and fine grinding, etc. However, there are still some problems after grinding, such as grinding marks, difficulties in further reducing the surface roughness and uneven distribution of surface roughness along the tooth profile. At present, gear profile polishing after grinding is one of the effective ways to solve the above problems. In this study, the main methods of tooth profile polishing are classified into electrochemical honing, abrasive flow machining, magnetorheological finishing and shear thickening fluids polishing. The machining principle of the current main gear tooth profile polishing methods is described in detail. Examples of various processing methods are listed. The advantages and problems of each machining method are summarized from the aspects of the range of machining adaptation, machining efficiency, the improvement rate of the surface roughness of the polished tooth profile and the requirements for the machining equipment. The results show that the combination of other auxiliary energy fields such as ultrasonic, laser and magnetic field with traditional polishing methods to achieve high efficiency, high precision and high surface consistency tooth profile polishing will be the main research direction in the future.关键词：Electro-chemical honing;Abrasive flow machining;Magnetorheological finishing;Shear thickening fluids polishing;Surface roughness;Processing efficiency
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发布时间：2023-12-21
Review
- 摘要：The accurate calculation of the backlash of harmonic reducers is crucial for the study of transmission performance, load capacity calculation, and tooth profile design of harmonic reducers. The current research is based on the neutral line no-elongation theory, calculating the assembly of flexible gear tooth profile. Considering the fact that gear teeth grow in the flexspline outer surface, assembly will make flexspline outer surface deform, leading to deviation of gear teeth. In this study, the method for solving the no-load clearance is proposed based on the flexspline outer surface deformation. The results show that the new method for calculating the flexspline assembly may present tooth profile interference, which should be considered in tooth profile design or harmonic reducer design. The finite element method is used to verify the analytical solution, and the two results are basically consistent.关键词：Flexible gear ring gear;Outer surface elongation;No-load backlash
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发布时间：2023-12-21 - 摘要：With the rapid development of robot industrialization and intelligence, welding robots are widely used in construction, machinery and other fields, and the motion performance and trajectory planning capabilities of robots directly affect the quality of welding. Aiming at this kind of problem, combined with the characteristics of series mechanism and parallel mechanism, a new type of six-degree-of-freedom (6DOF)series-parallel hybrid welding robot mechanism is designed. The standard D-H model is used to describe the relationship between the adjacent links of the robot, the kinematic model of the robot is established using the Matlab Robotics toolbox, the correctness of the parameters of the robot connecting rod is verified, and the working space of the robot is further calculated. At the same time, a trapezoidal function with parabolic transition is used to plan the end effector of the hybrid welding robot, and the multi-objective trajectory optimization scheme is proposed. The particle swarm optimization algorithm is used to optimize the time parameters, and the optimal time parameters that meet the positioning accuracy of the end of the welding machine manipulator are solved. The simulation results show that the optimized trajectory improves the stability and positioning accuracy of the hybrid welding robot, and lays a theoretical foundation for further vibration analysis and control of the robot.关键词：Hybrid welding robot;Kinematics;Trajectory optimization;Particle swarm optimization
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发布时间：2023-12-21 - 摘要：Firstly, based on the topological structure design method of the parallel mechanism, a two-translation and two-rotation (2T2R) parallel mechanism is designed. Its coupling degree is 1, and the position orientation characteristics （POC） set, constraint degree and degree of freedom are calculated. Secondly, the topological characteristic kinematics of the mechanism is analyzed, and the forward and inverse position solutions of the mechanism are solved, which verifies the correctness of the forward and inverse solutions. Finally, based on the inverse position solution, the singularity and workspace of the mechanism are analyzed and calculated, the possible singular position of the mechanism is obtained, and the maximum reachable space of the mechanism is obtained, which lay a foundation for the dynamics and dynamic balance research of the mechanism, as well as the manufacturing of the prototype.关键词：Parallel mechanism;Coupling degree;Singularity;Position orientation characteristics;Kinematics
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发布时间：2023-12-21 - 摘要：Aiming at the multi-objective optimization and trajectory planning problems of six-degree-of-freedom assembly robots, firstly, the atomic orbit search (AOS) algorithm is incorporated into the multi-objective optimization to construct the multi-objective optimization functions of time, energy consumption and shock. Secondly, the trajectory planning adopts the method of path point interpolation non-uniform rational B-spline curve, uses the AOS algorithm to determine the binding state and the binding energy of atoms, determines the candidate solution with the lowest energy level in the atom, outputs the optimal electron position, optimizes the Pareto value set space, and obtains the multi-objective optimized trajectory curve. Finally, the effectiveness of the proposed method is verified by the Matlab simulation. The results show that the trajectory planning method combined with the AOS algorithm can ensure that the assembly robot runs in the optimal route, which has certain engineering application value.关键词：Multi-objective optimization;Trajectory planning;AOS algorithm;Non-uniform rational B-spline curve
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发布时间：2023-12-21 - 摘要：A deep reinforcement learning (DRL)-based motion planning method is proposed to improve long planning elapse and lengthy path of the traditional planning algorithms for robotic manipulator movement in obstacle avoidance. Firstly, based on the mathematical model of the manipulator and the motion environment, the DOBOT robot and the operating environment are built in PyBullet, and the parameters such as the reward function, the action and the state variables required for DRL are set. Secondly, the deep deterministic policy gradient (DDPG) algorithm is applied for the characteristics of static obstacle avoidance, and motion simulation experiments are conducted. The simulation results show that the proposed DDPG algorithm has a certain degree of improvements in planning elapse and path length compared with the rapid-exploring random tree (RRT) algorithm and the improved RRT algorithm. Finally, the effectiveness of the DDPG algorithm in obstacle avoidance operations is tested using the DOBOT robot in a laboratory environment with multiple obstacles.关键词：Manipulator;Deep reinforcement learning;Obstacle avoidance path planning;Deep deterministic policy gradient algorithm
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发布时间：2023-12-21 - 摘要：The central axis fitting accuracy of the axis rotation method determines the absolute positioning accuracy of the calibrated robot. In this study, two kinds of axis fitting methods are used, and their fitting accuracies are analyzed. The first kind is the traditional fitting method, which fits the measuring point as a circle and uses the normal vector through the center of the circle as the axis of the robot. The second kind is the improved fitting method, which uses the measuring point to fit the sphere and plane, and obtains the intersecting circle of the fitted sphere and plane. In order to avoid the large geometric parameter calibration error caused by the small error of the over-center normal vector in the traditional method, the line of the center of the double intersecting circle is used as the axis of the robot. Compared with the fitting results of the laser tracker software, the fitted center of the intersecting circle has higher accuracy. The axis vectors of the first and the second axes are used, the axis vector of the first axis and the projection of the axis vector of the second axis on the vertical plane of the first axis are respectively used as the direction vector of the robot base coordinate system, and the conversion matrix of the measurement point from the measurement system to the robot system is constructed. By comparing the measurement point difference after conversion of the two conversion matrices, the conversion matrix using the second axis directly as the base coordinate system direction vector has a large measurement point conversion error.关键词：Robot kinematics;Axis rotation calibration;Fitting circle;Intersecting circle;Base coordinate system
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发布时间：2023-12-21
Theory·Research
- 摘要：In order to solve the problem of calculation efficiency and accuracy of time-varying meshing stiffness of spur bevel gears, a slice calculation method of meshing stiffness of spur bevel gears considering the coupling effect of tooth pairs is proposed. Based on the slice discretization method, the bevel gear tooth and the gear body are discretized into several slices with the same width along the tooth width direction and the axis direction respectively, and the slices are expanded based on the back cone equivalence principle. When the slice width is small enough, the bevel gear can be approximated as a series of spur gears, and the meshing stiffness of each slice can be calculated by the energy method. In order to consider the coupling effect of multi-tooth meshing, the correction coefficient of gear stiffness is introduced in the calculation of double tooth meshing stiffness, which reduces the calculation error of double tooth meshing stiffness. The meshing stiffness model of bevel gears under the error condition is established. The meshing stiffness of spur bevel gears, the angular displacement of the center point of each slice and the load distribution of the tooth surface under the ideal and assembly error conditions are calculated and analyzed. Finally, the accuracy and efficiency of the proposed method are verified by comparing with the finite element calculation results.关键词：Spur bevel gear;Time-varying meshing stiffness;Slicing method;Tooth pair coupling;Assembly error
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发布时间：2023-12-21 - 摘要：Based on the characteristics of the link structure and the rope pulley structure, a new reverse rope-pulley mechanism is proposed. The principle and motion characteristics of the new mechanism are introduced, and the structure of a three-knuckle manipulator with new mechanism for bag grabbing is designed. Firstly, the static analysis of the three-knuckle manipulator is carried out based on the method of equilibrium of plane forces. The accuracy of the static analysis is verified by Adams statics simulation, and the characteristic of higher force conversion rate is verified by the comparison and simulation with the link structure and rope pulley structure. Secondly, simplified modeling, kinematic envelope grasping simulation and static grasping contact force simulation are carried out for the three-knuckle manipulator. The mobile envelope grasping ability of the three-knuckle manipulator is shown by the simulation results. However, the disadvantage of uneven contact force distribution needs to be optimized for the current design.关键词：Underactuated mechanism;Cable-driven;Static analysis;Kinematic simulation;Static simulation
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发布时间：2023-12-21 - 摘要：With the increasing proportion of people with lower limb dysfunction in the population, lower limb exoskeleton, mainly in the form of physical assisted therapy, has become a research hotspot in the field of rehabilitation. In this study, a wearable lower limb exoskeleton prototype model is proposed and its motion performance is studied. Firstly, the corresponding relation between human lower limbs and exoskeleton is established. Secondly, the standard D-H method is used to build the exoskeleton kinematics mathematical model, the forward and inverse kinematics is solved through the homogeneous transformation matrix, and the correctness of the model and the solving equation is verified. Finally, the man-machine coupling model is simulated based on the gait characteristics of human lower limbs. The goodness of curve fitting shows that the exoskeleton runs smoothly, and has good compatibility and tracking performance. The joint curve data provides the data basis for the formulation of the control strategy of the lower limb exoskeleton.关键词：Lower limb exoskeleton;Structural design;Kinematic solution;Exoskeleton human coupling;Goodness of fit
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发布时间：2023-12-21 - 摘要：In this study, a hybrid type (2-PUR/UPS) &R cervical vertebra rehabilitation machine is proposed for the cervical traction rehabilitation training of patients with cervical spondylosis. The machine has 3R1T four degrees of freedom and meets the requirement of the range of motion of human cervical vertebra. The kinematic performance of the machine is analyzed to verify whether it can be applied in the field of human cervical vertebra rehabilitation. Firstly, the degrees of freedom of the mechanism are solved and verified by using the spiral theory and the modified Kutzbach-Grvble formula. Secondly, by solving the inverse solution of the position of the mechanism, the rod length of the mechanism is deduced, the program of solving the workspace is written, and the workspace of the mechanism is obtained by the numerical search method. Finally, the mechanism is simulated and analyzed by Adams software. The results show that the mechanism could reach the range required for cervical spine movement, including -55° to 35° for forward and backward leaning. Left-handed and right-handed is -52° to 52°; the left and right lateral flexion is -45° to 45°, which can provide traction treatment for patients with cervical spondylosis.关键词：Recovery machine;Cervical spine;Inverse solution;Workspace;Adams software
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发布时间：2023-12-21 - 摘要：The hemiplegic patients can't walk on their own due to the movement obstacle of one side of the lower limb caused by brain injury. The lower limb wearable walker can help them get the ability to walk, but if they want to walk out the normal gait like ordinary people, the gait planning of the lower limb wearable walker is necessary. Gait planning is the basis and key for man-machine coupling walking and maintaining stability. Firstly, through the analysis of the movement of each joint of the lower limb, the overall mechanism of the lower limb wearable walker is designed. Secondly the gait planning is carried out. The part between the joints of the leg of the walker is regarded as a homogeneous rigid link, nine special time points of each joint in the complete walking cycle are extracted, and the coordinates and angles of the joints at each time point are analyzed. Combined with the cubic spline interpolation method in Matlab software, the motion track of the joints is simulated. Finally,the gait planning data is analyzed to obtain the coordinates of the barycenter projection point, fit the motion track of the barycenter projection point, and analyze whether the track always falls in the support area. The results prove that the barycenter projection point is always in the supporting area, which indicates that the gait planning meets the stability requirements.关键词：Lower limb wearable walkers;Institutional design;Gait planning;Cubic spline interpolation;Stability;Barycenter projection point;Supporting domain
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发布时间：2023-12-21 - 摘要：Due to the interpenetrating layout of each shaft for the 6R robot, the movement of one joint could affect the other joints. This mechanical coupling could result in the interference of each joint, and an error between theoretical model and actual model would affect the absolute positioning accuracy of the robot. The motion compensation method obtained the coupling amount by measuring the error between the target value and the actual value and the joint angles are compensated. However, an active decoupling method of 6R robot based on Denavit-Hartenberg (D-H) parameters is provided. Firstly, the coupling of robot joints which is calculated through transmission analysis is added to the joint angle for 6R robot. Then, the D-H parameters with coupling are used in the forward kinematics, and the algebraic solution is used to obtain the inverse kinematics. The feasibility of the model is verified by the simulation of the workspace and kinematics through the Matlab robotic toolbox. At the same time, the simulation based on this method is built to compare with the motion compensation method. The above results prove that this method solves the motion coupling problems stemming from mechanical coupling, reduces the error of the robot end position and improves the robot positioning accuracy. Adding the linear coupling quantity to the joint variables does not significantly increase the calculation amount of kinematics for 6R robot, and the solution process is convenient.关键词：Transmission analysis;D-H parameters;Forward and inverse kinematics;Joint coupling
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发布时间：2023-12-21 - 摘要：Aiming at the lack of speed variators with large transmission ratio for the chain cold drawing production line, on the basis of the ZSY500-50 three-stage reducer, the technical contradiction existing in the technical system is analyzed using the TRIZ theory, and the invention principles that are conducive to solving the technical contradiction are found in the contradiction matrix table. Under the inspiration of the invention principles, the 50/100 second-speed gear transmission with reasonable and compact structure is designed by adding sliding gears, improving the sliding mechanism and optimizing the shafting layout. The strength calculation of the core components and the mechanical simulation using the Ansys Workbench software show that the core components of the two-speed variator all meet the strength requirements.关键词：TRIZ theory;Cold drawing;Large transmitting ratio;Speed variator
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发布时间：2023-12-21
Design· Calculation
- 摘要：The origami mechanism obtained by combining the origami art with the modern mechanism is widely used in the field of spatial structure, and its unique scalability, convenience, lightweight and miniaturization have always been research focuses. In this study, a thick plate clamping claw inspired by origami is proposed, and its design is analyzed. Firstly, the origami and mechanism are combined to design the shape, and the characteristics of a single degree of freedom are used to solve the problem of motion coordination and stability. Secondly, the kinematics of the thin gripper model is analyzed to explore the relation between the angle of rotation, twist angle and dihedral angle during its movement. Finally, considering the practical application of the project, the clamping jaws are thickened, and the relation between the input angle, the output displacement, and the clamping angle is analyzed. Different from the traditional gripper, the gripper has the characteristics of simple structure, high integration, and reliable movement performance, taking into consideration the flexible operation. It also has the ability to output a large clamping angle within a small input angle range. This study provides an important idea and reference for the research of deployable structure and grippers.关键词：Gripper;Origami;Thick origami;Kinematic analysis
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发布时间：2023-12-21 - 摘要：Fatigue performance of RV-20E reducers is investigated experimentally herein; load and life curves of RV-20E with different crankshaft heat treatment strengthening processes are obtained. The optimum surface microstructure and optimum surface hardness of the crankshaft for improving the fatigue life of the RV-20E reducer are analyzed, and the failure mode and failure mechanism of the crankshaft of the RV-20E reducer are discussed. Based on the S-N theory and the Miner theory, and combined with the force analysis of RV-20E, the life parameter of RV-20E reducers based on the crankshaft needle roller bearing assembly is derived, and the test data is compared and analyzed. The analysis and comparison show that the life parameter can effectively correlate the fatigue life of RV-20E reducers and can be used to predict the fatigue life of RV-20E reducers.关键词：RV-20E reducer;Crankshaft;Fatigue performance;Life analysis
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发布时间：2023-12-21 - 摘要：There are many kinds of distortion of carburizing and quenching gears, but they will be reflected in the grinding amount of gear flanks. Through theoretical analysis and long-term production practice, it is found that the change of tip diameter has the greatest influence on the grinding amount, the change of the helix angle and the circumferential warpage of gear rims takes the second place, and other factors have relatively little influence. The empirical formulas for calculating the maximum and minimum grinding amount of the tooth flank are given, according to the change of the tip diameter and other parameters. These formulas can be used to determine the case-hardened depth (CHD) in drawings, the reserved grinding amount of gear flanks during gear hobbing, and the target CHD during carburizing and quenching. After carburizing and quenching, the maximum and minimum grinding amount and the actual CHD can be calculated and predicted according to these formulas, so as to provide guidance for subsequent production.关键词：Carburizing and quenching;Distortion;Gear;Grinding amount;Case-hardened depth
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发布时间：2023-12-21 - 摘要：Aiming at the common key issues for gearbox vibration and noise, a certain type of subway car bogie gearbox has been regarded as the research object. The rigid-flexible coupling dynamics and vibration noise simulation model of the gearbox have been established by the LMS Virtual Lab software. The variable meshing stiffness, the dynamic bearing supporting load, the gearbox vibration, and the structural noise in the vicinity of the gearbox have been simulated and analyzed, and the vibration of the gearbox and the structural noise in the vicinity of the gearbox have been tested and verified. The results show that the time-varying meshing force of the helical gear pair of the subway car bogie gearbox and the dynamic load of the supporting bearing show a periodic fluctuation trend above and below a certain average value; the vibration of the gearbox body and the structural noise in the vicinity of the gearbox in the up and down, left and right direction are greater than those in the axial direction; the maximum relative errors between the simulated and experimental values of vibration and structural noise are respectively 14.61% and 3.77%, which can verify the rationality and correctness of the simulation analysis. The research provides a vibration and noise reduction for the theoretical basis and technical supporting of the subway vehicles and gearboxes.关键词：Metro vehicle;Bogie gearbox;Vibration;Noise;Coupling characteristic
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发布时间：2023-12-21
Test·Analysis
- 摘要：In view of the problem that the vibration stress of the axle driven bevel gear of an aeroengine exceeds the permissible stress, a spiral ring friction damper is designed for the bevel gear. In detail, a concave groove is fabricated on the inside rim of gear wheels, in which the designed spiral damping ring is embedded. The circumferential deformation of the spiral damping ring is inconsistent with the gear rim under working conditions; thus the mutual friction is induced and the vibration energy could be consumed. The designed spiral damper is applied to the vibration reduction scheme of an aeroengine bevel gear. The test results show that the spiral damping ring can effectively reduce the vibration stress level of the bevel gear.The vibration reduction efficiency of the first-order, 4-pitch diameter backward traveling wave resonant vibration is about 70.7%, and that of the first-order, 3-pitch diameter forward traveling wave resonant vibration is about 53.4%. Then the vibration stress level of the gear after vibration reduction satisfies the allowable stress. Moreover, the spiral damper enjoys convenience in installation and disassembly, and possesses small additional imbalance, which leads to a promising and broad application for vibration reduction of aeroengine gears.关键词：Bevel gear;Spiral ring damper;Friction damping;Vibration reduction;Vibration stress
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发布时间：2023-12-21 - 摘要：In order to obtain the static strength of small modulus plastic gears, a small modulus plastic gear static strength test bench is developed, which can accurately measure the static strength of plastic gears under different modulus, speeds and materials. The working principle, constitution and the design of tooling parts of the test bed are mainly introduced. The test bench is composed of the mechanical system, the electric control system and the measuring software. The electric control system and the measuring software mainly adopt the horizontal structure, which is of the compact structure, with small space occupation, uses simple fixture design and is easy to measure. The static strength test is carried out, and the static strength using different materials is briefly tested. The experimental equipment can realize the measurement of the static strength of the small module plastic gear, which solves the problems of inaccurate static strength test of the small module gear and the difficulty of test clamping, and provides theoretical value and practical application value for the design of the plastic gear in the future.关键词：Plastic gear;Test bench;Static strength;Limit load
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发布时间：2023-12-21 - 摘要：When using the process of metal powder injection molding (MIM) to prepare small module gears, in order to improve the quality and performance of the sintered parts of the gear, powder with different particle sizes is prepared. The sintering performance of the gear is analyzed by the melt flow meter, the porosity measurement software, the 2.5-dimensional image measuring instrument and the micro-Vickers hardness tester. The influence mechanism of particle sizes on the surface quality, porosity and shrinkage of gears is studied. The results show that due to the poor powder flow performance of the gear made of 5.0 μm powder, the powder concentration distribution is not uniform after sintering, there are black lines on the surface, and the dimensional shrinkage is not uniform, which affect the dimensional accuracy. Due to the poor sintering neck formation ability and slow diffusion process of the gear made of 9.0 μm powder, the porosity after sintering is high and the pore size is large. When the 7.0 μm powder is used to prepare the gear, the quality performance of the gear is the best. The gear has no surface defects, the porosity is reduced to 2.9%, the Vickers hardness value reaches 355, the shrinkage uniformity is high, the dimensional accuracy is high, and the accuracy of thetested items are better than class 7 according to the national standard GB 2363—1990.关键词：Metal powder injection molding（MIM）;Powder particle size;Surface quality;Porosity;Shrinkage
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发布时间：2023-12-21 - 摘要：By establishing the standard rack tool profile curve equation, using the VB.NET programming language to carry out secondary development in AutoCAD environment, the dynamic simulation program of the whole process of involute gears and root cutting is developed using the generating method to further study and explore the gear root cutting process and root cutting mechanism, and the maximum root cutting radius is accurately solved. The wrong conclusion that the maximum root cutting radius is equal to the distance between the center of rotation of the gear being machined and the intersection point between the top line of the tool teeth and the line of engagement is corrected. Based on this, the limiting conditions of the root cutting to the starting point of the working section of the big and small gear tooth profile and the interference at the root of the big and small gear are redetermined in the closed diagram selected by the displacement coefficient. Then the closure line chart of the modification coefficient selection can be drawn accurately.关键词：VB.NET;Dynamic simulation;Root tangent point;Root cutting radius;Root cutting mechanism
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发布时间：2023-12-21 - 摘要：In response to the current issues of wheel and shoe composite ladder wheelchairs, such as tire interference with the track, and collision between the wheelchair and the top platform during ladder climbing, a wheel shoe composite stair climbing wheelchair with a swing arm track chassis as the stair climbing mechanism and a new wheel shoe switching scheme is designed. Its mathematical model is established, the centroid coordinates, the vertical displacement curve of the center of mass for climbing stairs are analyzed, and the dynamic change curve of the swing arm motor and electric push rod during the four stages of wheel shoe switching are obtained. The up and down stairs mode and the wheel shoe switching mode of a wheelchair are simulated in RecurDyn software. The simulation results indicate that the wheelchair is smooth and safe during the process of ascending and descending stairs, and the theoretical values of the dynamics of the four stages of wheel shoe switching are consistent with the simulation situation. The research provides a theoretical basis for the mechanical structure design, electric push rod selection, and swing arm motor selection of this type of ladder wheelchairs.关键词：Wheel and shoe composite stair climbing wheelchair;Going up and down stairs;Wheel shoe switching;Simulation analysis
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发布时间：2023-12-21
Development·Application
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