Revolute Clearance Joints Research Articles

Dynamic characteristics of planar linear array deployable structure based on scissor-like element with differently located revolute clearance joints

This paper comprehensively investigates the parametric effects of differently located revolute clearance joints on the dynamic behavior of planar deployable structure based on scissor-like element. Considering the real physical mechanical joints, the normal and the tangential forces in the revolute clearance joints are respectively modeled using Flores contact-force model and LuGre friction model. The resulting forces and moments are embedded in the equations of motion of the scissor deployable structure for accurately describing the effect of joint clearance and governing the dynamic response of this structure. The effects of the main parameters such as the location of the clearance joint, the clearance size and the number of clearance joints on the dynamic characteristics of a multibody mechanical system have been numerically evaluated, and the results indicate that joints at different locations in a mechanical system have different sensitivities to the clearance size, and the more sensitive joint should be controlled to reduce the nonlinear behavior of this structure. Also, it can be concluded that the motion in one revolute clearance joint will affect the motion in the other clearance joints and the dynamic interaction of clearance joints is the important source of structural behavior change. Therefore, in order to accurately predict the dynamic responses of the mechanical system, the clearance effect of each joint on the multibody system should be investigated and understood.

Effects of restitution coefficient and material characteristics on dynamic response of planar multi-body systems with revolute clearance joint

To study the effects of restitution coefficient and material parameters on the dynamic characteristics of planar multi-body systems with revolute clearance joints, a comprehensive methodology for clearance revolute joints in a planar multibody system is presented and analyzed. A new nonlinear contact force model, which accounts for the axial length of bearing and has a wide suitable range of impact situation, is presented to evaluate the contact force between journal and bearing. Furthermore, a modified Coulomb friction force model also presented to consider the effect of friction in clearance joint. Then, a typical journal-bearing model and a planar slider-crank mechanism has revolute clearance joint are used as examples. From the main numerical results under the different restitution coefficient and material parameters, it can be concluded that coefficient of restitution has significant effects on dynamic response of multi-body systems with revolute clearance joint. Additionally, materials of journal and bearing with smaller Young’s modulus will cause obvious delay on dynamic response of multi-body systems.

Minimizing the influence of revolute joint clearance using the planar redundantly actuated mechanism

Joint clearance is unavoidable in real mechanism, so its effects should be minimized in order to fulfill the designed performances of the mechanism. In this paper, we proposed a method which is based on the redundantly actuated mechanism to minimize the influence of revolute joint clearance. A planar 3DOF redundantly actuated 4-RRR mechanism with 8 clearance joints is applied as an illustration to show how it works. Firstly, the kinematic and dynamic equations of the 4-RRR mechanism are established. Secondly, the joint clearance is geometrically described and the contact force models are introduced. After that, the joint clearances are restrained by preloading the passive links of the 4-RRR mechanism, the two-step Bathe integration method is used to solve these equations. Comparisons are made between the mechanisms with and without clearance restrain. Finally, experiments are carried out to verify the proposed method. Both simulation and experimental results show that the joint clearance can be successfully controlled by the redundantly actuated mechanism. The performance of a redundant 4-RRR parallel mechanism with joint clearances is studied.A method is proposed to minimize the effects of clearance based on redundant mechanism.Both simulation and Experiment verified the effectiveness of the proposed methodology.

A numerical coupling model for a multibody system with multiple lubricated clearance joints

In machines and mechanisms, most of the clearance joints are designed to operate with lubricant fluid, which is an effective way of ensuring better performance of the mechanical systems. The differently located lubricated joints interact with each other, influencing the total performances of the mechanical system. In this study, a numerical coupling model for the dynamics and lubrication analyses of the multibody system with multiple lubricated clearance joints is established. This approach couples the dynamics model of the multibody system with the lubrication models of translational and revolute clearance joints. The dynamics model is established by the Lagrange’s method, while The lubrication models are solved using the finite element method. The hydrodynamic forces built up by the lubricant fluid are evaluated from the motion states of the system and then input into dynamics model of the multibody system. Finally, the proposed approach is applied to a four-stroke gasoline engine with the lubricated piston skirt-liner subsystem and lubricated bearing at the big end of the connecting rod.

A continuous analysis method of planar rigid-body mechanical systems with two revolute clearance joints

In this paper we are interested in the dynamic behavior of a slider-crank mechanism with single and two revolute clearance joints. Due to the clearance existence in the revolute joints, it is important to choose an appropriate contact force model in analyzing the dynamic response of a slider-crank mechanism with clearances. The dynamic equations are established by combining the Newton–Euler equations with modified contact force model and improved Coulomb friction force model, and the Baumgarte stabilization approach is used to improve the numerical stability. According to numerical and experimental results, the method of continuous contact can be verified to be reasonable. Comparing dynamic the response between one clearance joint and two clearance joints in a crank-slider mechanism, it is easy to find a significant mutual coupling region due to the presence of two clearance joints by simply contact figures. The dynamic response in a mechanism with two clearance joints is not a simple superposition of that in mechanism with one clearance joint. Therefore, all the joints in a multibody system should be modeled as clearance joints.

Computational prediction and experimental validation of revolute joint clearance wear in the low-velocity planar mechanism

Within the multibody dynamics framework, the paper proposed an efficient procedure to calculate revolute joint wear of planar mechanism with low velocity. Firstly, based on the wear test data, a method to calculate the wear coefficient that corresponds to the actual working condition of the mechanism is proposed. Then, an efficient iterative prediction method for joint clearance wear evolving in the multibody dynamic system in is proposed based on the Archard's wear model. Meanwhile, the wear tests of the typical mechanism have verified the method proposed in this paper. The research shows that when the increments of the wear depth of revolute joints are not big, the method can provide high prediction accuracy; however, as the predicted wear depth increases, the prediction error increases as well.

A differential approach for modeling revolute clearance joints in planar rigid multibody systems

A non-penetration approach of frictional contact analysis is presented for modeling revolute clearance joints of planar rigid multibody systems. In the revolute clearance joint, the motion modes of the journal are divided into three categories, namely, the free motion, collision, and permanent contact modes. The switch between different contact modes is identified by the state of the journal and bearing, including the gap and the normal relative velocity. When impact in the revolute clearance joint is detected, the collision process is simulated by the impulse-based differential approach, where Stronge’s improved model for restitution is employed to determine the relative velocity after impact. Instead of algebraic equations, the impact process is described by a set of ordinary differential equations (ODEs), which avoids solving complementarity problems. Moreover, in the permanent contact mode, the constraint-based approach and modified Coulomb’s friction law are adopted. The permanent contact mode maintains for most of the time and the governing ODEs are non-stiff. There is general agreement that the constraint-based approach is more efficient than the force-based method. A slider–crank mechanism with a revolute clearance joint is considered as a demonstrative application example where the comparison with the continuous contact force model is investigated.

Bifurcation in a planar four-bar mechanism with revolute clearance joint

Generally, multi-body mechanical systems in which the impact phenomena occur exhibit chaotic and quasi-periodic behavior. Mechanisms with clearance joint are categorized in such systems due to contact between the connecting bodies. In this paper, we would investigate the nonlinear dynamic behavior of a four-bar mechanism with joint and clearance at the connection between the coupler and rocker. Motion equations are derived based on the Lagrangian approach. The nonlinear continuous contact force model proposed by Lankarani and Nikravesh is utilized to evaluate the normal contact force developed in the journal–bearing system. Furthermore, the friction effect on the clearance joint is considered using a modified Coulomb friction law. The dynamical behaviors are numerically identified in discrete state space, based on the Poincare portraits. Numerical simulations display both periodic and chaotic motions in the system behavior. Therefore, bifurcation analysis has been performed with a change in the size of clearance corresponding to the various values of crank rotational velocities. Then, we compare some clearance ranges, in which the system response becomes stable for these cases. Fast Fourier transformation is also applied to analyze the frequency spectrum of the system response.

Dynamic characteristics of planar linear array deployable structure based on scissor-like element with joint clearance using a new mixed contact force model

This paper aims at investigating precisely the dynamic performance of deployable structure constituted by scissor unit mechanisms with clearance joint. Based on the motion law in real joints, the contact model is established using an improved Gonthier nonlinear continuous contact force model, and the friction effect is considered using LuGre model. Moreover, the resulting contact force is suitable to be included into the generalized force of the equations of motion of a multibody system and contributes to replace motion constraints. In the sequel of this process, the effect of joint clearance is successfully introduced into the dynamical model of scissor deployable structure and the dynamic characteristics of deployable structure with joint clearance are obtained using a direct default correction method, which can directly modify the coordinates and speed of the system to avoid the numerical results divergence. Also, the new hybrid contact force model of revolute joint clearance is verified through comparing with the original model. The numerical simulation results show that the improved contact model proposed here has the great merit that predicts the dynamic behavior of scissor deployable structure with joint clearance.

Dynamic responses of space solar arrays considering joint clearance and structural flexibility

This article numerically investigates the effects of revolute joint clearance and structural flexibility on the overall dynamic characteristics of a deployable solar array system. Considering torque spring, close cable loop configuration, and lock mechanism, a typical mechanism composed of a main body with a yoke and two panels is used as a demonstration case to study the effects of clearance and flexibility on the dynamic response of the deployable solar array system in the deployment and lock process. The normal contact force model and tangential friction model in clearance joint are established using Lankarani Nikravesh model and modified Coulomb friction model, respectively. The numerical simulation results reveal that the coupling of clearance and flexibility makes different effects on the dynamic characteristics of the deployable space solar arrays for different operation stages. Besides, the clearance and flexibility of a mechanical system play crucial roles in predicting accurately the dynamic response of the system, which is the foundation of mechanism design, precision analysis, and control system design.

A study on dynamics of planar multibody mechanical systems with multiple revolute clearance joints

Abstract In this work, the dynamic responses of multibody mechanical systems including multiple revolute clearance joints are investigated numerically. The joint components of an imperfect joint with clearance are modeled as contact bodies. The normal force in the revolute clearance joint is modeled using a continuous contact force model, which is based on the elastic Hertz theory together with a dissipative term. The friction effect is considered using a modified Coulomb friction model. Then the dynamics equation of multibody systems with clearance joint is established. Finally, a planar four-bar mechanical system with multiple revolute clearance joints is utilized as demonstrative application example to perform the investigation. The main results of this work can be drawn that clearances in joints play a crucial role in predicting accurately the dynamic responses of multibody mechanical systems and the multiple clearance joints interact strongly with one another.

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.

The effects of joint clearance on the dynamics of the 3RRR planar parallel manipulator

SUMMARYIn reality, clearances in the joints are inevitable due to tolerances, and defects arising from design and manufacturing. Therefore, poor dynamic performance, reduction in components component lifetimes and generation of undesirable vibrations result in impacts of mating parts in the clearance joint. In this study, the dynamic behavior of a planar mechanism with revolute joints, in the presence of clearances is investigated. A continuous contact force model, based on elastic Hertz theory together with a dissipative term, is used to evaluate the contact forces here. Moreover, using a contact model, the effects of working speed and clearance size on the dynamic characteristics of a planar mechanical system are analyzed and compared. Furthermore, numerical results for a 3RRR planar parallel manipulator with six revolute clearance joints are presented.

Planar roller chain drive dynamics using a cylindrical contact force model

ABSTRACTA multibody dynamics methodology for the study of roller chain drives, which includes the use of a continuous cylindrical contact model, is used here to investigate the influence of energy dissipative factors on the drive dynamics. The chain drive mechanisms are described as a planar multibody system in which the connection between each pair of links is modelled as a multiple revolute clearance joint, instead of the traditional kinematic constraint, and the meshing between the roller and sprocket teeth is also treated as a generalized revolute clearance joint. The contact force model includes the geometric contact detection and the contact force evaluation, which in turn includes energy dissipative features resulting from the friction and restitution coefficients terms used in the model. Recognizing the numerical and physical limitations of the existing cylindrical contact models, an enhanced cylindrical contact model is applied here and demonstrated with the study of the dynamics of a roller chain drive with varied initial pre-tensions and energy dissipative coefficients.

Dynamic analysis of mechanical systems with planar revolute joints with clearance

Clearances in mechanical joints are unavoidable due to many uncertainties such as manufacturing tolerances, assemblage, wear, and material deformation. The dynamic characteristics of mechanical systems are greatly affected by the joint clearances during the contact process. Thus, a proper contact force model plays a key role in simulating the overall performance of the mechanical systems. In this paper, a hybrid contact force model is described, which is based on the Lankarani–Nikravesh contact force model and the elastic foundation model. The discrete element theory and Gaussian quadrature are utilized to analyze and simulate the contact process. By distributing the non-uniform bearing points over the pin surface and calculating the penetration of each point individually, the total contact force can be obtained by integrating the discrete ones in the contact area. Some comparisons with the Lankarani–Nikravesh model indicate that the hybrid model is more effective for small clearance and low restitution coefficient situations. Finally, comparison of dynamic characteristics between the numerical simulation results and experimental ones for a revolute clearance joint in the slider–crank mechanism is employed to validate the hybrid model.

Dynamic analysis of planar mechanisms with revolute clearance joints based on two evaluation indices

ABSTRACTJoint clearance is one of the most important factors that influence the dynamic performance of a mechanical system. In this study, a quantitative analysis method, which contains two clearance effect evaluation indices that can better evaluate influence of clearance joints on the dynamic performance of the mechanisms, is proposed. A dynamic modeling approach of planar mechanisms with clearance joints is introduced. A crank-slider mechanism with multiple clearance revolute joints is studied to support the proposed analysis methodology. Besides, different dynamic responses generated by different materials of the clearance joints are also investigated based on the clearance effect evaluation indices.

Dynamics of chain drives using a generalized revolute clearance joint formulation

Roller chain drives can be modeled as a constrained dynamic system composed of a large number of rigid bodies, links, rollers and sprockets, interconnected by multiple ideal or clearance revolute joints. Here, the methodology described for a clearance revolute joint, usually used in the contact between the pin link/bushing link and the bushing link/roller pairs, is generalized to describe the roller/sprocket tooth surface contact pair. Regardless of whether the clearance revolute joint is used for roller–sprocket or bushing–sprocket engagements, depending on the chain type, the contact conditions are defined as a function of the tooth geometry. The methodology describing the tooth profile and allowing for the contact detection uses a tooth fixed coordinate system to evaluate all quantities required by the contact force model. As the contact phenomenon is herein described using the continuous contact force method, the contact force in each contact pair is available at any time during the dynamic simulation.

Bifurcation in planar slider–crank mechanism with revolute clearance joint

Generally, dynamic systems with clearance exhibit a chaotic and quasi-periodic behavior, and the main concern of the design engineers is to achieve the range of stability for such systems. In this research, nonlinear dynamic behavior of a slider–crank mechanism with clearance has been studied. Differential equations of motion are derived considering clearance in the revolute joint between the slider and connecting rod. The normal contact force developed in the journal-bearing system is calculated using the continuous contact force model proposed by Lankarani and Nikravesh. Furthermore, the incorporation of the friction effect on the clearance joint is performed using the Ambrósio model. Using the Poincaré portrait corresponding to non-autonomous systems, dynamic behavior of the mechanism is shown in discrete space, which is the criterion for the detection of chaos. Bifurcation analysis has been studied with varying clearance sizes, corresponding to two different values of crank angular velocity; then some intervals in which the periodic orbit embedded in the system response becomes stable are computed. Sensitive dependence of such multi-body mechanical systems on clearance size is also explained based on the bifurcation diagrams.

Nonlinear Behavior Analysis of a Flapping-Wing Mechanism with Clearance Joint

The nonlinear behavior of a flapping-wing mechanism affected by revolute joint clearance is studied in this work. Considering the axial dimension of bearing, energy dissipation and the nonlinear power exponent from material, the nonlinear stiffness coefficient and an improved contact dynamic model in the joint clearance is established. A flapping-wing mechanism dynamic model with joint clearance is also established. Then embed the contact dynamic model and system dynamic model into the mechanical system simulation software package. From large numbers simulations performed, and the analysis of journal trajectories and Poincare maps under the different clearance sizes, it can be concluded that flapping-wing mechanism with joint clearance exhibit a chaotic response, and the more clearance size, the more obvious chaotic behavior.