Wear clearance is a predominant failure mode in multibody systems. To address the challenges associated with the high costs of data acquisition in complex systems, a novel motion function reliability assessment framework based on deep learning principles under small samples is designed to analyze the reliability degradation induced by irregular wear clearances. Initially, the dynamic model of the Dual-Drive Multi-Link System (DDMLS) considering irregular wear clearances is derived through a combination of the Lagrange method and the Archard wear model, and the correctness of this model is substantiated through experimental validation. Subsequently, an error model for uncertain system is proposed, and an error prediction method under small samples is developed utilizing deep neural network (DNN), with the effectiveness of the DNN model demonstrated through numerical examples. Finally, leveraging this model, the reliability degradation behavior of the DDMLS considering wear clearances is analyzed using the stress-strength interference theory (SSIT). Unlike traditional structural reliability methods, this study focuses on the reliability degradation of motion functions in multibody systems caused by wear. The main contribution of this research lies in the application-driven and integrative approach, emphasizing a new problem formulation and system-level application, providing a practical solution for the reliability study of mechanical systems under small samples.

This study develops a dynamic model for the transmission system of industrial robots, specifically focusing on the six-bar mechanism with both revolute and translational clearances. The hybrid clearances, which occur due to unavoidable manufacturing tolerances or intentional design for flexibility, can negatively impact the accuracy, efficiency, and stability of the system. To address these challenges, a surrogate model is created for the mechanism's maximum displacement error and mass parameters using the Back Propagation Neural Network (BPNN). This model captures the complex relationship between the system's parameters and performance. Subsequently, an optimization model is developed using the artificial bee colony (ABC) algorithm, which explores the parameter space efficiently to improve the mechanism's dynamic behavior. The optimization process leads to a significant enhancement in the mechanism's dynamic response, reducing vibration and improving the motion accuracy. These findings contribute to the optimization of six-bar mechanism in industrial robots, offering a practical solution for enhancing transmission performance, system reliability, and operational stability in robotic applications.

Degradation phenomena, such as joint clearance corrosion in Landing Gear Retraction and Extension System (LGRES), significantly compromise the motion accuracy and reliability of system. To thoroughly investigate these adverse effects, this paper introduces an integrated method that synergizes multi-body dynamics analysis with non-probabilistic reliability analysis to evaluate the reliability of LGRES under the influence of joint clearance corrosion. Firstly, a multi-body dynamics model of the LGRES is established, incorporating the impact of joint clearance corrosion. Secondly, a novel Chebyshev Polynomial Approximation-Gradient Boosted Decision Tree Regression (CPA-GBDTR) method is proposed to quantify the propagation of interval uncertainty within the complex dynamics of the system. The efficacy of this method is substantiated through rigorous numerical examples. Thirdly, a non-probabilistic reliability assessment model based on Stress-Strength Interference Theory (SSIT) is developed, complemented by a non-probabilistic reliability evaluation method utilizing Importance Sampling. Finally, based on the established evaluation framework, the non-probabilistic reliability of the LGRES is analyzed. This research not only furnishes innovative insights into the reliability analysis of LGRES but also serves as a pivotal reference for the non-probabilistic reliability evaluation of other intricate mechanical systems.

The wear of rotating pair is a significant factor for the failure of mechanical systems. Currently, some scholars have undertaken investigations on wear clearance, but these works often concentrate on basic systems with even wear clearance, while investigations on multibody systems with uneven wear clearances remains scarce. In addition, the research on wear clearance often focuses on theoretical exploration and computer simulation, while the test research is relatively few. Therefore, a modeling method for 9-bar mechanism with multiple uneven wear clearances is derived by using the Archard model and Lagrange method, the effects of wear times and initial clearance values on dynamic characteristics and nonlinear dynamics of mechanism considering uneven wear clearances are investigated. The test bed of 9-bar mechanism considering clearances is designed and the validity of the theoretical model has been confirmed through a comparison between the collected test data and theoretical data. This paper supplies theory for accurately predicting the dynamic characteristics of multibody system containing uneven wear clearances, and provides proof for identifying and repairing the design defects of mechanism.

This paper proposes a new optimization method by immune algorithm to reduce the impact of clearance joint and wear on the dynamics of mechanisms. Firstly, the dynamic model of crank-slider mechanism is built by Lagrange principle, and the wear phenomenon of clearance joint is characterized by Archard model. Then, the motion function reliability model of mechanism is presented by Stress-Strength interference (SSI) theory. Secondly, the optimization model of mechanism is derived and the surrogate model of the maximum contact force of clearance joint is indicated by response surface method (RSM), the immune algorithm is used to find the optimal solution of the surrogate model. Finally, the impact of wear and optimization on dynamic behavior, nonlinear dynamics, and motion function reliability of mechanism is investigated. The results show that wear clearance joint seriously affects the performance of mechanism. After optimization, the dynamic behavior and nonlinear dynamics of mechanism are improved, and the motion function reliability of mechanism is increased. This paper raises foundation for predicting the performance of mechanisms considering wear clearance joint, and provides theoretical guidance for optimization design and fault diagnosis of mechanisms.

Atmospheric corrosion poses a significant challenge for the components of aircraft exposed to prolonged harsh weather conditions, critically impacting the safety property of aircraft landing gear retraction mechanism (ALGRM). This paper focuses on the ALGRM of a specific aircraft type, presenting a new modeling and analysis approach to assess the influence of atmospheric corrosion on dynamic behavior and nonlinear characteristics of mechanism. Initially, the dynamic model of ALGRM incorporating clearance joints is established using Lagrangian method. Numerical solutions are then obtained using the Runge-Kutta method. Subsequently, COMSOL simulation software is employed to simulate the corrosion morphology of the bearing under atmospheric corrosion, integrating the corroded bearing surfaces into the dynamic model of the mechanism. Finally, the study investigates the effects of corrosion time and different bearing materials on the dynamic behavior and nonlinear characteristics of ALGRM considering atmospheric corrosion. The results indicate that as corrosion time increases, the degradation of the dynamic behavior of ALGRM becomes more pronounced, and there are significant variations for corrosion morphology of bearing made of different materials under atmospheric corrosion. The findings of this study contribute to a broader understanding of the complex interactions between the dynamic behavior of aircraft and environmental degradation, providing some insights for designing ALGRM that are more durable and adaptable to atmospheric corrosion environments.

The extreme conditions severely constrain the dynamic characteristics of aircraft landing gear retraction mechanism (ALGRM). This paper proposes a dynamic modeling and analysis method for ALGRM considering the coupling effects of extreme conditions such as clearance joints, flexible rods, and salt spray corrosion. Firstly, the mathematical model for clearance joint and flexible rod is established and the dynamic model of ALGRM considering clearance joints and flexible rods is formulated based on Lagrangian equation. Furthermore, the salt spray corrosion model for clearance joint is developed using COMSOL simulation software. Finally, the effects of different temperatures and relative humidities on the corrosion depth of clearance joint and the dynamic characteristics of ALGRM under the coupling effects of extreme conditions are investigated. The results have found that the impact of extreme conditions on dynamics of system cannot be ignored. This study not only provides a theoretical foundation for predicting the dynamic characteristics of ALGRM under extreme conditions but also offers insights for the optimization design and corrosion protection efforts of landing gear.

Extreme working conditions pose a serious challenge to the functionality, longevity, and reliability of mechanical systems; however, current research on the reliability of mechanical systems under these conditions is very limited. Consequently, this study proposes a methodology for modeling and analyzing the dynamic precision reliability of the aircraft landing gear retraction mechanism (ALGRM) under coupled extreme conditions such as high temperature, high humidity, and salt spray corrosion. First, an improved Kriging (I-K) model is proposed by optimizing the hyperparameters of the traditional Kriging (T-K) model via the artificial fish swarm algorithm (AFSA), and two cases are used to demonstrate that the I-K model has higher prediction precision. Second, a mathematical model of clearance joint is built, and the corrosion characteristics of motion joint under extreme working conditions are simulated using COMSOL software. The Lagrange method is applied to establish the dynamic model of the ALGRM considering multiple random variables. Finally, the limit state function is derived between the random variables and the extreme output response of the ALGRM via the I-K model. The dynamic precision reliability model for the ALGRM under coupled extreme working conditions is solved using the first order second moment (FOSM) method and the parameter sensitivity is evaluated. This study contributes some insights into the modeling and evaluation of the reliability of mechanical systems under coupled extreme working conditions, thereby enhancing the broader understanding of mechanical reliability theory.

In the operation of mechanisms with lubricated clearances, uncertain parameters such as the temperature of lubricant, driving speed, and clearance value will lead to dynamic variations for oil film thickness of lubricated clearance. The lubrication may fail when the oil film thickness of bearing surfaces is insufficient, thereby significantly affecting the performance of the mechanism. This paper presents a novel method for the dynamic reliability of lubricated clearances by improved response surface method (IRSM). Firstly, the mathematical model of lubricated clearance is established, and the oil film load of lubricated clearance is defined, then the dynamic model of mechanism considering lubricated clearances is built through Lagrange method. Secondly, considering the failure mechanism of the lubricated clearance, the surrogate model is established using the IRSM with minimum oil film thickness as the failure criterion. Finally, taking the 9-link mechanism with multiple lubricated clearances as a numerical example, the dynamic minimum oil film thickness of the lubricated clearance considering uncertain parameters is computed. The reliability of the lubricated clearance is investigated by the surrogate model, and the applicability of the model is verified by the Monte Carlo method (MCM). The results demonstrate that the IRSM has higher accuracy compared to the traditional response surface method (TRSM). This paper provides a theoretical basis for the study of failure mechanism and reliability of lubricated clearances, and also has practical significance for engineering applications.

In order to explore the effect of lubrication clearances and flexible components on motion accuracy reliability of mechanism, this paper takes the six-link mechanism as research target, the mathematical model of lubrication clearance is established, the flexible rod element model is built by absolute node coordinate formulation (ANCF) method. A method for the motion accuracy reliability of mechanism is derived based on Stress-Strength interference theory, taking into account random parameters such as dynamic viscosity, cross-sectional area, Young's modulus and clearance values. The influence of driving speed on motion accuracy reliability of mechanism is analyzed. The results indicate that as the driving speed increases, the motion accuracy reliability of mechanism continuously decreases.

汽车座椅骨架在整体构型以及零件组成方面相似度很高,适合利用计算机辅助技术进行变型设计.在对汽车座椅进行模块划分后,利用CATIA二次开发的CAA技术设计了一款汽车座椅骨架快速变型设计软件,并连接数据库,通过人机交互的可视化界面完成座椅差异化零件的参数化建模.使用CAA的装配API对参数化后的零件及其他配套零件完成座椅整体的自动装配.该设计缩短了汽车座椅开发的准备时间,提高了汽车座椅骨架的设计效率和设计质量.

A calculation method of tooth root stress for large transmission ratio gear and rack is proposed using a broken-line section model and thermal-mechanical coupling analysis. To describe the transient meshing dynamics between the gear and the rack, a contact deformation model between the gear and the rack is fitted by using the least square method, and the meshing temperature field is calculated using the Blok flash temperature theory. The method of the broken-line section is modified based on the fatigue crack growth path at the tooth root. A new broken-line section model to calculate the tooth root stress is established, and a stress permeability factor is introduced to identify the width of the broken line. Using the meshing temperature field of gear and rack, the calculation formulas of root bending stress and root compression stress are derived by the integral-iterative method under thermal-mechanical coupling, and the correctness of the maximum tooth root stress model is validated by the finite element method (FEM). Compared with other methods for analyzing the thermal strength of gear roots, the proposed novel broken-line section method has simpler calculations and higher accuracy, and it can systematically analyze the effect of structural parameters on the dynamic strength of gear transmission mechanisms under actual working conditions.(c) 2022 Elsevier Inc. All rights reserved.

In this paper, the design defects of the cam transmission mechanism is produced by defects in the geometric characteristics, such as curvature interference of contact surface and unreasonable pressure angle, which greatly affect the dynamic behaviors. In order to avoid the shortcomings of traditional design methods, surface family envelope theory is used to fit the profile curve of the cam curve groove. Through analyzing the defect characteristics(curvature interference and unreasonable pressure angle) of the cam curve groove, the self-contained defect identification algorithms are proposed. To systematically identify whether the cam curve groove has design defects, a complete algorithm based on the selfcontained defect identification algorithms is designed. Finally, the feasibility of the identification algorithm is validated by numerical examples. The numerical examples are validated by the finite element method and computerized numerical control machining. The results reveal that curvature interference is generally not produced if the appropriate processing method is adopted, and the design of the component size directly determines whether the pressure angle defect occurs. Compared with fault diagnosis of cam mechanism, the proposed self-contained algorithms show simpler calculations and higher accuracy, and it can also properly analyze the effect of design parameters on the dynamic behavior of cam transmission mechanism. (c) 2022 Elsevier Inc. All rights reserved.

In medium or small-sized spacecrafts’ docking process, it’s feasible to adopt a flexible probe for the probe-cone docking mechanism instead a buffer to reduce the docking impact force. The governing equations of kinematics and dynamics are derived from Lagrange analytical method. The influence parameters of the impact force are separated by simplifying the impact mathematical modeling. The effects of the influence parameters in the impact force, such as the length of docking beam, and the material of the docking mechanism, are discussed by finite element method. The varation amplitude and varation frequency are obtained by docking experiment, and reliability and correctness of the analysis reuslts are verified.

A minimum contact stress modification method for profile curve design defects in a beam-spring-cone docking mechanism (BSCDM) based on genetic algorithm is presented in this paper, the profile curve and contact position of BSCDM are optimized. Under low-speed conditions, an improved elastic contact model of semi-space elastic bodies is established to modify and optimize the elliptic profile envelope curve based on Hertz contact theory and two kinds of complete elliptic integral, the improved contact model is used to solve elastic contact problems with the geometric characteristics of the ellipse surface, the optimal profile curve of the docking joint and the optimal docking contact point position are obtained. The results of numerical simulation and the experiment demonstrate the feasibility and validity of above models and methods.

Under the low-velocity impact conditions, in order to study the contact load variation law of the ellipsoid elastic bodies, an elastic–plastic contact analysis model of rough ellipsoid surfaces is provided based on elastic–plastic fractal theory. A spherical elastic–plastic fractal model considering friction factors is established, and the spherical diameter density distribution function and elastic contact mechanics are used as the solution methods. The two contact surfaces are taken as the research object, and the influence of relevant variables on the contact intensity is analyzed. The analysis results show that the fractal dimension and roughness have a greater effect on contact performance, the contact load is positively related to the surface roughness, and the lower friction coefficient has a weaker effect on the contact load, and the correctness of the present model is verified by comparing finite element simulation results and other studies. The modified spherical contact load function provides a theoretical basis for the friction and wear of the microscopic surface, it can be applied for solving the sliding contact problems with different impact velocities and the surface bearing capacity of the impact parts can be improved.

When using parallel manipulators as machine tools, the spherical joint has been widely used and replaced by a combination of a universal joint and a rotating unit, but the introduced differences and effects have not been studied in detail. In this paper, an approach to establish the mathematical models of the ideal and combined spherical joints is presented, and the differences between the two spherical joints are given from the perspective of constraints, workspace, clearance, and contact deformation. First, the non-interference workspace of a class universal joint is investigated by using a simple and clear projection method, where the constraint domain and workspace of two spherical joints are proposed. Next, the approximate clearance models of these two spherical joints are analyzed, and the corresponding contact deformation models are also given based on the Hertzian Contact theory. Finally, a 1PU + 3UPS parallel manipulator is used to verify the discrepant effects of two spherical joints on parallel manipulators. If the combined spherical joint is used, the results indicate that the improvement in the workspace is significant, but the drop in stiffness is also evident. Thus, this paper provides a theoretical basis for researchers to use combined spherical joints.

The accuracy of the vibration model used in the design process directly affects the vibration performance of a parallel robot in practice, which determines the machining accuracy and the surface finish of the manufactured products. Considering a drilling parallel robot with a passive branch and few degrees of freedom as the implementation object, a vibration modelling method is proposed in which Kane’s equation is utilized, and various commonly ignored factors, such as the passive branch, the joint clearances and gravity, are considered. To explore the effects of the passive branch, which was considered ideal in previous studies, two dynamic models are derived in which the passive branch is rigid or flexible. To explore the effects of the joint clearances, which were ignored in previous studies, two stiffness models of branches are derived, in which the joint clearances are considered or ignored. Finally, numerical examples are presented for analysing the effects of these commonly ignored factors on the vibration performance of the drilling parallel robot. Regarding to the effects of these commonly ignored factors, the findings of this paper can serve as a reference for designers in simplifying the vibration model in the design process of parallel robot.

SummaryWhen using parallel manipulators as machine tools, their stiffness is an important factor in the quality of the produced products. This paper presents an overall approximate stiffness model for a heavy-load parallel manipulator, which considers the effects of actuator stiffness, joint clearance, joint contact deformation, and limb deformation. Based on the principle of virtual work and the introduced modified parameters, the proposed overall compliance matrix successfully takes four factors into a unified expression. To obtain the overall compliance matrix, the approximate stiffness models of the joint clearance, joint contact deformation, and limb deformation are given. In addition, by combining the statistical simulation including the random uncertainties and the proposed approximate stiffness models as the basis of the magnitudes for each random variable, an approach based on the expected trajectory and external load is also proposed for stiffness defect identification such that the estimation is more accurate and reliable. Finally, a numerical example of the 1PU+3UPS parallel manipulator and a discussion are presented to demonstrate the practicability of the proposed stiffness model and defect identification approach. After modifying the structure parameters of the defective components, the prototype experiences a significant stiffness improvement.

In order to improve the machining efficiency and the flexibility of manufacturing system, the study of multi-duty parallel manipulators has attracted the interest of some researchers. In this paper, according to the effects of different operations on the driving element, a demarcation diagram for distinguishing different duties, such as statics, low-speed but heavy-load, high-speed but low-load and high-speed but heavy-load, is proposed, and a defect identification approach to prevent the occurrence of defects for multi-duty parallel manipulators is presented. Taking the 1PU+3UPS parallel manipulator as an instance, an analysis method to the statics and dynamics is investigated by means of the screw theory and the proposed virtual screw. Based on the numerical example, the results show that the classification and practicability of operations can be accurately identified by the proposed demarcation diagram and defect identification approach, respectively.