Joint Clearance Research Articles

Dynamic characteristics investigation of variable stator vanes mechanism considering mixed clearances

The Variable Stator Vanes (VSV) mechanism enhances the stability margin of aero engines by adjusting the vane angles to prevent surging, but the clearances of kinematic joint will affect rotation accuracy of vanes. To investigate the dynamic characteristics of VSV mechanism that simultaneously consider spherical clearance and three-dimensional (3D) rotational joint clearance, an analytical method was developed to study the dynamic characteristics of VSV mechanism Vanes considering mixed clearance. Firstly, a dynamic model incorporating mixed clearances is developed and validated experimentally. Then, the effects of different clearance types, clearance sizes, and mixed clearances are analyzed on the dynamic characteristics of the vane. Finally, the results indicate that an increase in clearance leads to a greater susceptibility of the dynamic characteristics being affected. Taking into account the effects of mixed clearances on dynamic characteristics, which are not merely a straightforward summation of the impacts of two types of clearances, it is crucial to consider the interplay between different types of clearances. The study provides a basis for the modeling and dynamic characteristics analysis of VSV mechanisms taking into account mixed clearances.

A novel multidisciplinary hierarchical collaborative optimization of the high-speed pantograph considering the uncertainty of joint clearances

The pantograph–catenary system is a critical subsystem of the train power supply system. However, the increasing train speed brings many challenges. In particular, the interaction impacts of different disciplines are intensified. To solve the optimization problem of the high-speed pantograph, a multidisciplinary hierarchical collaborative optimization (MHCO) method is proposed in this article. MHCO divides the subsystem-level optimization process of design variables into various layers based on the shared design variables between disciplines. At the overall system level, the consistency constraint condition is constructed to obtain optimal values according to the optimized subsystem-level results. Four optimization indicators [translational motion of the pantograph head, pantograph lightweighting, pantograph–catenary contact force (PCCF) and active control] are established to conduct he design optimization of a high-speed pantograph. Compared with the initial value, the four indicators have improved by 78.7076%, 16.6516%, 38.1037% and 15.5542%. MHCO provides a new method for designing complex mechanical systems.

Influence of dynamic complexity on serial robots with joint clearance based on a nonlinearity measure

Conditional monitoring and diagnosis of serial robots depend not only on the method used but also on the dynamic complexity of the robotic system itself. Previously, researchers have focused mainly on the analysis of dynamic behaviors with different parameters of a mechanical system with clearance. Although the indicators such as Root Mean Square (RMS), spectrum kurtosis (SK), Entropy have the potentiality to express the specific trend by different parameters, it can be noticed that they mainly depend on the values of the dynamic responses and neglect the information of the nonlinear characteristics in the responses of mechanical systems. In this paper, a nonlinearity measure-based method is proposed to analyze the impact of dynamic complexity on serial robots with joint clearance. The kinetic equations of a serial robot with joint clearance are established by considering the contact forces in the joint. The dynamic model of the robotic system is validated by experiments. A quantization method for dynamic complexity analysis is established based on the nonlinearity measure, and the influences of parameters on the dynamic complexity are analyzed via numerical computations for the validated dynamical models of the robotic system. A relationship is developed among the clearance radius, friction coefficient, and dynamic complexity. This shows that a larger clearance radius will lead to a more complex system and that friction coefficients within a certain range can reduce the dynamic complexity of the system. These results can guide methodological choices for condition monitoring and diagnosis of serial robotic systems.

Modeling and analysis of nonlinear dynamics of axisymmetric vector nozzle based on deep neural network

Abstract The axisymmetric nozzle mechanism is the core part for thrust vectoring of aero engine, which contains complex rigid-flexible coupled multibody system with joints clearance and significantly reduces the efficiency in modeling and calculation, therefore the kinematics and dynamics analysis of axisymmetric vectoring nozzle mechanism based on deep neural network is proposed. The deep neural network model of the axisymmetric vector nozzle is established according to the limited training data from the physical dynamic model and then used to predict the kinematics and dynamics response of the axisymmetric vector nozzle. This study analyses the effects of joint clearance on the kinematics and dynamics of the axisymmetric vector nozzle mechanism by a data-driven model. It is found that the angular acceleration of the expanding blade and the driving force are mostly affected by joint clearance followed by the angle, angular velocity and position of the expanding blade. Larger joint clearance results in more pronounced fluctuations of the dynamic response of the mechanism, which is due to the greater relative velocity and contact force between the bushing and the pin. Since axisymmetric vector nozzles are highly complex nonlinear systems, traditional numerical methods of dynamics are extremely time-consuming. Our work indicates that the data-driven approach greatly reduces the computational cost while maintaining accuracy, and can be used for rapid evaluation and iterative computation of complex multibody dynamics of engine nozzle mechanism.

Dynamic performance optimization of a planar mechanism with cam clearance joint based on non-uniform rational B-spline and reinforcement learning

Dynamic performance optimization of a planar mechanism with cam clearance joint based on non-uniform rational B-spline and reinforcement learning

Multiple lubricated joints with long and short bearings in multibody mechanical systems - Modeling, simulation, and performance analysis

This study examines the effect of multiple lubricated imperfect long and short bearings on the performance of a multibody mechanical system. Unlike the typical assumption of a single perfect or imperfect lubricated joint due to modeling difficulties, this research considers the practical impacts of clearances in multiple joints. While unlubricated joints generally cause significant performance issues, lubricants reduce these effects, creating more localized peaks. The findings show that as the number of lubricated joints increases, both the magnitude and frequency of these peaks rise. In systems with multiple journal bearings, torque peaks become more noticeable due to the additional degrees of freedom introduced by the clearances. These degrees of freedom amplify acceleration, leading to higher lubricant reaction forces, which in turn require greater motor torque peaks to maintain the system's kinematics. Shorter lubricated joints exhibit more severe peaks than longer ones, mainly due to side leakage causing axial pressure variation and reduced damping capacity. The study highlights the need to replace idealized joints with imperfect ones for more accurate modeling of practical systems.

Optimization Acceleration and Contact Force of Space Slider-Crank Mechanism with Spherical Clearance Joints

Optimization Acceleration and Contact Force of Space Slider-Crank Mechanism with Spherical Clearance Joints

Kinematic Reliability of Manipulators Based on an Interval Approach

Robotic manipulators inevitably experience the impact of uncertainties and errors, such as dimensional tolerances and joint clearances. Therefore, this paper proposes a novel method based on an interval approach to evaluate the kinematic reliability of manipulators. Kinematic reliability quantifies the probability of positioning errors that fall within allowable boundaries. As a result, reliability evaluates the probability that the interval end-effector error produced by dimensional tolerances exceeds an acceptable rate. The proposed reliability index is based on the interval error that conveys an alternative approach to the kinematic reliability methods based on probabilistic frameworks reported in the literature based on probabilistic approaches. The obtained numerical results demonstrate the viability of the proposed methodology by evaluating the reliability of a serial manipulator subjected to joint clearances and a parallel manipulator with dimensional tolerances.

Simultaneous optimal system and controller design for multibody systems with joint friction using direct sensitivities

AbstractReal-world multibody systems are often subject to phenomena like friction, joint clearances, and external events. These phenomena can significantly impact the optimal design of the system and its controller. This work addresses the gradient-based optimization methodology for multibody dynamic systems with joint friction using a direct sensitivity approach. The Brown–McPhee model has been used to characterize the joint friction in the system. This model is suitable for the study due to its accuracy for dynamic simulation and its compatibility with sensitivity analysis. This novel methodology supports codesign of the multibody system and its controller, which is especially relevant for applications like robotics and servo-mechanical systems, where the actuation and design are highly dependent on each other. Numerical results are obtained using a software package written in Julia with state-of-the-art libraries for automatic differentiation and differential equations. Three case studies are provided to demonstrate the attractive properties of simultaneous optimal design and control approach for certain applications.

Deployment dynamics of the solar array system with clearance joints considering interval uncertainties

Deployment dynamics of the solar array system with clearance joints considering interval uncertainties

Reliability evaluation of folding wing system with lubricated joint clearances considering multiple reliability indicators

Reliability evaluation of folding wing system with lubricated joint clearances considering multiple reliability indicators

An enhanced continuous contact force model for deployable structures with clearance joints: Validation, simulation, and dynamic characteristics

An enhanced continuous contact force model for deployable structures with clearance joints: Validation, simulation, and dynamic characteristics

Compound control method for reliability of the robotic arms with clearance joint

Compound control method for reliability of the robotic arms with clearance joint

Development and investigation for rigid-flexible coupling dynamic performances of the morphing wing with clearance joints

Morphing wings have enjoyed much research interest due to their advantages in improving aircraft adaptability to various service environments. A single drive and continuous variable bending morphing mechanism with multiple configurations is proposed. The morphing wing designed based on this mechanism can have the advantages of lightweight, multiple configurations and smooth morphing shapes. Transient aerodynamic loads will destroy the dynamic performance of the wing during the multi-mode morphing process. Therefore, it is crucial to analyze the vibration characteristics for the reliability of the morphing wing. However, it is difficult to obtain its dynamic model and solution because of the complex configuration and the multi-mode morphing. In this paper, a mathematical model for the multi-mode morphing of the morphing mechanism based on lockable joints is described using the constraint equation firstly. Then, a rigid-flexible coupling dynamic model of the morphing wing with clearance joints is established. Finally, the influence of the infective joint and the flexible link on the vibration properties of the morphing wing is analyzed in detail. Moreover, differences in the dynamic parameters between rapid and regular actuation are discussed. The results obtained in this paper have an important engineering value for the design and manufacture of the morphing wing.

A Hyperbolic Contact Surface Winkler Contact Force Model for Spherical Clearance Joints

Abstract Spherical clearance joints are essential for the successful deployment of space structures. When the clearance is small enough, the contacts will be considered conformal contact, which probably leads to inaccuracies in existing contact force models. To address the limitation, this paper proposes a novel hyperbolic contact surface Winkler model. First, a new fundamental formula incorporating a modified variable exponent is presented. Based on the surrogate modeling method, an optimized surrogate function for the variable coefficient is developed. In the optimization process, the finite element and response surface methods (RSMs) are introduced to improve the precision and reliability of the model. Compared with previous models, this paper organizes a detailed discussion and evaluation to validate the accuracy and application of the new proposed model, after which a dynamic example demonstrates the model's effectiveness. The results highlight the model's accuracy and practical efficacy, showing a strong correlation and minimal margin of error, especially when compared to finite element method (FEM) results. This improvement is attributed to the refined variable exponent, which accurately characterizes the relationship between contact force and penetration depth, and the optimized variable coefficient, which fine-tunes the contact force magnitude. Additionally, the model's versatility extends beyond the geometric properties of the contact bodies, offering a broad application scope. As a foundation of precise impact modeling, it is crucial to address the structural dynamic challenges inherent in high-precision space structures.

THE INFLUENCE OF SMALL CLEARANCES IN THE SPHERICAL JOINTS OF THE SYSTEMS ON THEIR DYNAMIC RESPONSE

The paper highlights the influence of small clearances in the spherical joints on their natural frequencies and modes of vibration. Joints with bearings made of materials that involve low friction in the coupling (Teflon and HDPE polyethylene) were considered.Two cases of coupling by means of the spherical joints were considered, namely: the coupling angle of the bars in the spherical joint being of 00 and of 900, respectively.The size of the clearance influences the first natural frequency of the system in the sense of decreasing it, but also in the modification of the vibration modes of the system when even a small clearance appears in the joint.

Comprehensive accuracy analysis for large closed-loop deployable structures based on matrix structure analysis and linear-complementarity-based contact analysis of spatial joint clearances

The surface accuracy of the deployable structure is crucial in determining the electromagnetic performance of the large satellite antenna. This paper proposes a comprehensive accuracy analysis framework for deployable structures considering clearances of spatial joints, geometric deviations, elastic deformations, external loads, and preloads, all of which can affect surface accuracy during the assembly process. Surface accuracy is calculated by combining the global equilibrium analysis of the deployable structure with the local equilibrium analysis of clearance-affected joints. First, a global elastostatic equilibrium analysis of the deployable structure is performed based on a unified mathematical formulation that describes the elasticity of beams and joints. Then, the local equilibrium analysis for the clearance-affected joints is transformed into a quadratic optimization problem through a linear-complementarity-based method. This method avoids the necessity for a combinatorial search for several traditional discontinuous contact configurations. Considering both global and local equilibrium in iterative analysis, the surface accuracy of the antenna is calculated. This integration avoids prior artificial assumptions about contact configurations of the joints. Finally, the proposed method is validated by comparing it with simulations and experimental results.

Rigid-flexible coupling dynamic modelling and dynamic accuracy analysis of planar cam four-bar mechanism with multiple clearance joints

Combination mechanism of conjugate cam and four-bar is a complex type of multi-body system, in which the coupling problems such as cam profile law, flexible deformation of connecting rods, and multiple joint clearance collision make it difficult to model and optimise its dynamics. Just as the beating-up mechanism of high-speed rapier looms for multi-layer weaving is a representative conjugate cam four-bar mechanism. In response to the current development of textile machinery in the direction of high-speed and precision, and in order to improve the work efficiency and operational accuracy of the conjugate cam four-bar beating-up mechanism, the following work is done for the purpose of taking into account the multi-joint clearance and the flexible rod based on the mechanism. Firstly, based on Kane's equation, a multi-body dynamic model with multiple clearances is established combined with clearance collision theory. Secondly, a dynamic model of a rigid-flexible coupling system with multiple revolute clearances is established using finite element method combined with modal synthesis technology. Subsequently, the variables separation method and mode superposition method are used to solve the dynamic equations of the coupled system. Finally, numerical examples are used to analyse the effects of clearance quantity, clearance size, mode truncation order, cam speed, and component material properties on the dynamic response and accuracy of the system. The results show that, in the rotational speed range of 600–800 rpm, the dynamic performance of the system is little affected by the speed; Through comparative analysis of multiple materials, it is found that selecting carbon fibre composite materials has the smallest impact on the motion accuracy of the system. In this paper, the clearance collision model, finite element model and rigid-flexible coupling dynamic model are integrated, which are applied to the cam-linkage combined multi-body mechanism, and the dynamic problems of the actual machine are analysed and solved.

Research on Spatial Developable Mechanism Considering Revolute Clearance Joints with Irregular Rough Surfaces

Due to assembling, manufacturing errors, and wear, irregular rough surfaces inevitably exist in joints, which will increase the contact stiffness nonlinearity at the joint of the spatial developable mechanism, and the traditional contact force model is difficult to accurately predict the contact force change of irregular rough surface clearance. Aiming at the difficulty of accurately predicting the dynamic behavior of the spatial developable mechanism caused by rough joint clearance, an improved clearance contact force modeling method based on an uncoordinated contact model is proposed in this paper. The influence of rough peak distribution on the contact area is analyzed. The stiffness of the traditional Hertz model is modified based on the probability distribution density function of the rough peak, and an improved contact force model based on dynamic contact stiffness is established. Based on the Lagrange multiplier method, the dynamics model of spatial developable mechanism is constructed. Based on the model, the dynamic analysis of the spatial expansion mechanism is carried out, and the influence of the roughness of the contact surface and the size of the clearance on the dynamic characteristics of the system are explored; as well, the influence of different clearance parameters on the dynamic characteristics of the development mechanism is revealed. Through the analysis, this paper provides a theoretical basis for predicting the effect of a spatial revolute clearance joint on the dynamic characteristics of the mechanism and lays a good foundation for the manufacture and application of the mechanism.

Research on fruit picking test of blueberry harvesting machinery under transmission clearance

Since China possesses the vast territory and a large blueberry planting area, blueberry harvesting with hand is laborious and time consuming. As the blueberry planting agronomy in China is different from other countries, it is pretty significant to develop blueberry harvesting machinery applicable to the domestic planting agronomy to achieve mechanized harvesting of blueberries. In blueberry harvesting operation, the harvesting system as the core component of the machine is the key technology of the harvesting machinery. The previous study found that: in terms of harvesting machinery, most of the literature has studied the dynamic characteristics, while few articles have been published to study the transmission clearance. But the clearance collision force generated by the transmission clearance of the harvesting system directly affected the output load moment and harvesting force of the machine developed by acting on the plant, and then affected the picking efficiency and the quality of picked fruit. Therefore, this paper focuses on the study of the transmission clearance of the blueberry harvesting machine. Firstly, the MLSD modeling method was applied to establish the transmission clearance model of the harvesting device, and the corresponding mechanical analysis of the transmission clearance was carried out. Secondly, after programming in MATLAB software and simulation in ADAMS software, the correctness of the transmission clearance model of the harvesting device was verified in different environments. The multi-body dynamics analysis software ADAMS was used for building the transmission clearance model of the harvesting device and perform mechanical simulation to analyze the clearance collision force and the output load moment of the harvesting device. Pro/E, ADAMS and ANSYS software were integrated to establish the flexible body of blueberry plant. Then the flexible body was combined with the mechanical model of harvesting device for rigid-flexible coupling simulation analysis to study the fruit harvesting force under different transmission clearances. Finally, the orthogonal method was used to conduct field test on blueberry harvesting to study the influence of the transmission clearance on the quality of picked fruit and picking efficiency of the machinery. Therefore, the best combination of the transmission clearance of the harvester was obtained as follows: cam clearance (the clearance joints of cam) was 0.25 mm, the slider clearance was 0.2 mm, left connecting rod clearance pair was 0.1 mm, right connecting rod clearance pair was 0.2 mm; the field picking test was conducted to obtain the machine's picking efficiency was 3.93 kg min−1, the shedding rate of unripe fruit was 3.1 %, and the damage rate of picked fruit was 2.8 %. The research findings of this paper can offer referenced basis and theoretical support for berry harvesting machinery, and also can provide guidance for the design and improvement of other agricultural and forestry harvesting machinery.