Lubricated Revolute Joints Research Articles

Failure analysis of a lock mechanism with multiple dependent components based on two-phase degradation model

Failure analysis of a lock mechanism with multiple dependent components is studied. Wear of the lubricated revolute joints in the mechanism presents the characteristic of multi-phase due to the change of degradation mechanism. It is not suitable to govern the degradation by stochastic processes only considering single phase pattern. In this paper, a change-point Wiener and Inverse Gaussian process is modeled to capture the two-phase degradation of the revolute joints. And the degradation parameter estimation based on Bayesian method is addressed. Since the wear evolution of the joints in the mechanism is affected by the same influence random variables, there exists dependence between them, and Vine Copula is utilized to describe the dependence. Besides, the time-varying dependence between the degradation processes is also investigated. Then, the reliability of the lock mechanism is obtained, and the result shows that the time-varying dependent model can more accurately describe the reliability curve of the system. Finally, in order to quantify the contribution of each degrading component on the system failure probability, the component importance measure is extended dynamically, through which the revolute joints can be ranked so that the weakest joint will be identified afterwards.

Interface reduction methods for mechanical systems with elastohydrodynamic lubricated revolute joints

In this contribution, three different reduction methods for elastic structures with lubricated interfaces are presented and compared with each other. While for the first two methods, classical reduction strategies from component mode synthesis are applied, for the third method, a dual reduction basis is used, consisting of vibration modes of the free floating structure, attachment modes and residual modes. Within this new dual approach, it is shown how the residual modes can be obtained by applying pressure distributions of analytical solutions of the hydrodynamic equations. The described methods are compared for two classical simulation example—for a one-sided elastohydrodynamic lubricated joint of a slider–crank mechanism in a floating frame of reference formulation as well as for an elastic rotor in a flexible journal bearing.

Tracking Accuracy Analysis of a Planar Flexible Manipulator With Lubricated Joint and Interval Uncertainty

A method for trajectory tracking accuracy analysis of a two-link flexible manipulator with lubricated revolute joint involving interval uncertainty is presented. In this method, first, fuzzy self-tuning proportion integration differentiation (PID) control is applied to track the desired tip trajectory of the manipulator. The absolute nodal coordinate formulation (ANCF) is employed for the finite element discretization of the flexible manipulator. And lubricated revolute joint is modeled based on the infinitely short journal bearing with Gümbel conditions. Second, uncertainty of clearance size is considered, and interval analysis method is applied. Numerical simulation is posted to investigate the cushioning effect of lubricants on the clearance and influence of uncertainty on control accuracy of the manipulator. The results show that the lubricants can improve the stability of motion and operation precision of the manipulator; however, uncertainty of the manipulator may reduce the control accuracy of the manipulator.

A new numerical method for planar multibody system with mixed lubricated revolute joint

A new method for modeling and analysis of planar multibody systems with lubricated revolute joints is presented. This method is established by coupling the lubrication model of lubricated revolute clearance joint with the dynamics model of multibody system. The lubrication model is solved by the Finite Element Method, while the multibody dynamics equations are established by Lagrange's method. In order to take into account the effects of the surfaces roughness on the hydrodynamic lubrication when the oil film between the mating surfaces has a very small thickness, the average Reynolds equation is adopted. The hydrodynamic forces built up by the lubricant fluid are evaluated from the knowledge of the system variables and then included into the dynamics equations of the multibody system. In the end, the proposed approach is applied to the piston–connecting rod–crank system in a four-stoke gasoline engine with lubricated clearance joint at the big end of the connecting rod. The clearance size and lubricant viscosity are investigated so as to reveal their influences on both the dynamics and lubrication performances. From the main obtained results, it can be concluded that the use of lubricant at mechanism joints is an effective way to ensure better performance. Within a given range, the cases with smaller clearance or higher lubricant viscosity are conducive to maintaining the stability of the motion of mechanism, and will decrease the friction power loss.

Modeling and analysis of planar multibody system with mixed lubricated revolute joint

By coupling the mixed lubrication model of a lubricated revolute clearance joint with the dynamics model of multibody system, this study presents a new methodology for modeling and analysis of planar multibody system with mixed lubricated revolute joints. The lubrication model is solved by the Finite Element Method, while the multibody dynamics equations are established by Lagrange׳s method. The hydrodynamic forces built up by the lubricant fluid are evaluated from the knowledge of the system variables and then included into the equations of motion of the multibody system. In the end, the proposed approach is applied to the piston–connecting rod–crank system in a four-stoke gasoline engine with lubricated clearance joint at the small end of the connecting rod.

Influence of the Hip Joint Modeling Approaches on the Kinematics of Human Gait

The influence of the hip joint formulation on the kinematic response of the model of human gait is investigated throughout this work. To accomplish this goal, the fundamental issues of the modeling process of a planar hip joint under the framework of multibody systems are revisited. In particular, the formulations for the ideal, dry, and lubricated revolute joints are described and utilized for the interaction of femur head inside acetabulum or the hip bone. In this process, the main kinematic and dynamic aspects of hip joints are analyzed. In a simple manner, the forces that are generated during human gait, for both dry and lubricated hip joint models, are computed in terms of the system's state variables and subsequently introduced into the dynamics equations of motion of the multibody system as external generalized forces. Moreover, a human multibody model is considered, which incorporates the different approaches for the hip articulation, namely, ideal joint, dry, and lubricated models. Finally, several computational simulations based on different approaches are performed, and the main results are presented and compared to identify differences among the methodologies and procedures adopted in this work. The input conditions to the models correspond to the experimental data capture from an adult male during normal gait. In general, the obtained results in terms of positions do not differ significantly when different hip joint models are considered. In sharp contrast, the velocity and acceleration plotted vary significantly. The effect of the hip joint modeling approach is clearly measurable and visible in terms of peaks and oscillations of the velocities and accelerations. In general, with the dry hip model, intrajoint force peaks can be observed, which can be associated with the multiple impacts between the femur head and the cup. In turn, when the lubricant is present, the system's response tends to be smoother due to the damping effects of the synovial fluid.

Investigation on the influence of the cavitation boundaries on the dynamic behavior of planar mechanical systems with hydrodynamic bearings

The characterization of lubricated revolute joints configures a topic of great interest in mechanisms and machines since there is a significant demand for its proper design in many applications. Therefore, this work proposes a solution for the evaluation of the hydrodynamic force components of the journal bearings obtained from the integration of the Reynolds equation for infinitely short bearings. The main difficulty in obtaining these hydrodynamic forces lies on adequately defining the boundary conditions of the Reynolds equation. Differently from the boundary conditions proposed in classical literature, this work presents an approach to determine the integration boundaries, i.e., the angular position in the bearing reference system where the pressure is null. Therefore, the hydrodynamic forces are calculated taking into account only the positive pressure. These angles are time dependent, and its evaluation is very important for a more accurate estimation of the hydrodynamic force components. The computer simulations are accomplished for different length–diameter ratios (L/D). From the global results, it can be concluded that the proposed approach is promising to efficiently represent the hydrodynamic conditions in bearings with L/D ratios up to 0.5.

A novel transition model for lubricated revolute joints in planar multibody systems

The dynamic behavior and the life of machineries are greatly affected by lubricated clearance joints,which are inevitable in mechanical systems, whereas investigations on lubricated clearance joints are very limited due to the difficulty in coupling lubrication theory with dynamics. By analyzing the transition status and considering the hydrodynamic lubrication, elasto-hydrodynamic lubrication, and partial lubrication and contact a novel transition model for the lubricated clearance joint is proposed to tackle with the transition between the lubrication statuses and the contact status. With the novel transition model, we performed numerical dynamic simulations based on a slider crank mechanism with a lubricated clearance joint. Using the novel transition model and the existed transition model (Flores model) in numerical simulations, we obtained and compared dynamic results, which demonstrate that the novel transition model is more accurate, efficient, and feasible than the Flores model.

Kinematics and Dynamics of Mechanical Systems with Lubricated Revolute Joints: the Infinitely-Short Journal-Bearing Approach

This paper deals with a methodology to assess the influence of the lubricated revolute joints in the kinematics and dynamics of mechanical systems. The existence of the clearance at revolute joints is inevitable in all mechanical systems and most of them are designed to operate with a lubricant fluid. In the present work, the infinitely-short journal-bearing approach for dynamic loads is used to evaluate the resulting hydrodynamic forces of the pressure distribution in the lubricated revolute joints. These hydrodynamic forces are then introduced into the system’s equations of motion as external applied forces. A numerical example is presented in order to demonstrate the efficiency and accuracy of the methodology and procedures adopted in this work. The numerical results point out that the existence of lubricated joint can affect the kinematics and dynamics of system.

Model reduction of a flexible multibody system with clearance

A system reduction scheme related to a flexible multibody system with clearance is devised. In this work, the absolute nodal coordinate formulation is used to model the flexible multibody system, while imperfect joint is modeled as dry clearance joint or lubricated revolute joint. Meanwhile, the component mode synthesis is applied to reduce the size of the matrices. Finally, numerical examples are posted to analyze the proper selection of component modes and the convergence properties of the model reduction technique. It is obvious that the results of the reduced model are close to the results of the original model when the error of the maximum deformation energy between the reduced model and the original model is very small. The results of the reduced model with lubricated revolute joint can achieve high calculation accuracy with fewer modes than those with dry clearance joint.

The effect of the lubricated revolute joint parameters and hydrodynamic force models on the dynamic response of planar multibody systems

In this work a comprehensive methodology for dynamic modeling and analysis of planar multibody systems with lubricated revolute joints is presented. In general, this type of mechanical systems includes journal-bearings in which the load varies in both magnitude and direction. The fundamental issues associated with the theory of lubrication for dynamically loaded journal-bearings are revisited that allow for the evaluation of the Reynolds equation for dynamic regime. This approach permits the derivation of the suitable hydrodynamic force laws that are embedded into the dynamics of multibody systems formulation. In this work, three different hydrodynamic force models are considered, namely the Pinkus and Sternlicht approach for long journal-bearings and the Frêne et al. models for both long and short journal-bearings. Results for a planar slider–crank mechanism with a lubricated revolute joint between the connecting-rod and slider are presented and utilized to discuss the assumptions and procedures adopted throughout the present study. Different test scenarios are taken into account with the purpose of performing a comparative study for quantifying the effect of the clearance size, lubricant viscosity, input crank speed and hydrodynamic force model on the dynamic response of multibody systems with lubricated revolute joints. From the global results obtained from computational simulations, it can be concluded that the clearance size, the lubricant viscosity and the operating conditions play a key role in predicting the dynamic behavior of multibody systems.

On the influence of a pin type on the friction losses in pin bearings

The aim of this paper is to analyze lubricated revolute joints from the viewpoint of friction losses. The paper deals with the lubricated revolute joints composed of a pin and two more elements connected by means of the pin. It is considered here how different pin types affect friction losses in pin bearings. Three existing pin types are investigated: a pin press-fitted either in the first or in the second element or the one free to rotate in both elements. As a measure of friction losses, a dissipation function is determined in all three cases. Using the results obtained, the advantages of using the full-floating pin with respect to two other types are demonstrated by means of a numerical example.

Simulation of planar flexible multibody systems with clearance and lubricated revolute joints

Modeling of clearance joints plays an important role in the analysis and design of multibody mechanical systems. Based on the absolute nodal coordinate formulation (ANCF), a new computational methodology for modeling and analysis of planar flexible multibody systems with clearance and lubricated revolute joints is presented. A planar absolute nodal coordinate formulation based on the locking-free shear deformable beam element is implemented to discretize the flexible bodies. A continuous contact-impact model is used to evaluate the contact force, in which energy dissipation in the form of hysteresis damping is considered. A force transition model from hydrodynamic lubrication forces to dry contact forces is introduced to ensure continuity in the joint reaction force. A comprehensive study with different lubrication force models has also been carried out. The generalized-α method is used to solve the equations of motion and several efficient methods are incorporated in the proposed model. Finally, the methodology is validated by two numerical examples.

Lubricated revolute joints in rigid multibody systems

The main purpose of this work is to present a general methodology for modeling lubricated revolute joints in constrained rigid multibody systems. In the dynamic analysis of journal-bearings, the hydrodynamic forces, which include both squeeze and wedge effects, generated by the lubricant fluid, oppose the journal motion. The hydrodynamic forces are obtained by integrating the pressure distribution evaluated with the aid of Reynolds’ equation, written for the dynamic regime. The hydrodynamic forces built up by the lubricant fluid are evaluated from the system state variables and included into the equations of motion of the multibody system. Numerical examples are presented in order to demonstrate the use of the methodologies and procedures described in this work.

Modelling lubricated revolute joints in multibody mechanical systems

This work deals with the modelling of lubricated revolute joints in multibody mechanical systems. In most machines and mechanisms, the joints are designed to operate with some lubricant fluid. The high pressures generated in the lubricant fluid act to keep the journal and the bearing apart. Moreover, the thin film formed by lubricant reduces friction and wear, provides load capacity and adds damping to dissipate undesirable mechanical vibrations. In the dynamic analysis of journal-bearings, the hydrodynamic forces, which include both squeeze and wedge effects, produced by the lubricant fluid oppose the journal motion. These forces are obtained by integrating the pressure distribution evaluated with the aid of Reynolds' equation written for the dynamic regime. The hydrodynamic forces are nonlinear functions of journal centre position and velocity relative to the bearing centre. In a simple way, the hydrodynamic forces built up by the lubricant fluid are evaluated from the state of variable of the system and included into the equations of motion of the mechanical system. Results for an elementary slider-crank mechanism, in which a lubricated revolute joint connects the connecting rod and slider, are used to discuss the assumptions and procedures adopted.

Dynamic Analysis for Planar Multibody Mechanical Systems with Lubricated Joints

The dynamic analysis of planar multibody systems with revolute clearance joints, including dry contact and lubrication effects is presented here. The clearances are always present in the kinematic joints. They are known to be the sources for impact forces, which ultimately result in wear and tear of the joints. A joint with clearance is included in the multibody system much like a revolute joint. If there is no lubricant in the joint, impacts occur in the system and the corresponding impulsive forces are transmitted throughout the multibody system. These impacts and the eventual continuous contact are described here by a force model that accounts for the geometric and material characteristics of the journal and bearing. In most of the machines and mechanisms, the joints are designed to operate with some lubricant fluid. The high pressures generated in the lubricant fluid act to keep the journal and the bearing surfaces apart. Moreover, the lubricant provides protection against wear and tear. The equations governing the dynamical behavior of the general mechanical systems incorporate the impact force due to the joint clearance without lubricant, as well as the hydrodynamic forces owing to the lubrication effect. A continuous contact model provides the intra-joint impact forces. The friction effects due to the contact in the joints are also represented. In addition, a general methodology for modeling lubricated revolute joints in multibody mechanical systems is also presented. Results for a slider-crank mechanism with a revolute clearance joint between the connecting rod and the slider are presented and used to discuss the assumptions and procedures adopted.

Dynamic analysis of flexible linkages with lubricated joints

The dynamic behavior of flexible linkages with lubricated revolute joints is investigated, with consideration of elastic deformation, bearing clearances and hydrodynamic lubrication. An inertial frame based approach to elastic linkage dynamics yields equations of motion in a form amenable to finite element formulations. Non-linear stiffness and damping characteristics are used to obtain impact forces at revolute joints. Pressure caused by hydrodynamic lubrication is calculated by using a finite difference method. Illustrative examples are shown to compare vibratory behaviors of idealized, clearanced, squeeze film lubricated and hydrodynamically lubricated flexible linkages.