Friction Force Model Research Articles

Effective Locomotion and Precise Unclogging Motion of an Untethered Flexible-Legged Magnetic Robot for Vascular Diseases

We propose an untethered flexible-legged magnetic robot (FLMR) manipulated by an external rotating magnetic field (ERMF) to generate effective locomotion and precise unclogging motion to treat vascular diseases. The proposed FLMR is composed of a front body with a drill tip, a cylindrical permanent magnet, a rear body, and flexible legs. The flexible legs are obliquely attached to the bodies like blades of a propeller, so that the FLMR can generate propulsive force in a fluidic environment for locomotion and unclogging motions. To provide manipulation guidelines for locomotion and unclogging motions, we developed a dynamic model of propulsive force, axial force, and friction force, and we established a control method of propulsive force according to the rotating frequency of the ERMF and the diameter of the tube, based on the proposed dynamic model. Finally, we prototyped the FLMR and conducted several experiments to verify its navigation performances and the control method of the propulsive force. Also, we conducted an in vitro experiment with a pseudo blood clot to demonstrate the validity of the locomotion and unclogging motions of the FLMR.

Dynamic analysis for vertical soft landing of reusable launch vehicle with landing strut flexibility

Based on oleo-honeycomb dampers, a 6-DOF vertical soft landing dynamic model for reusable launch vehicle considering landing strut flexibility is constructed. In order to better analyze the lateral deflection and friction force of the “cantilever beam” type landing strut, a new model for strut is incorporated. Static analysis is first performed based on the rotation angle compatibility equations to attain the equivalent inertia moment. Then the strut lateral vibration model and friction force model are obtained by simplifying it as viscoelastic beam with a tip mass. After that, the ADAMS models are established to perform the comparison and verification analysis of the 6-DOF dynamic model. The results show that the results of 6-DOF dynamic model can approximately approach to the results of rigid-flex coupling model established in ADAMS. Furthermore, the research of the influence of assembly gap between cylinders and bearings, bearing’s elastic modulus, friction coefficient and initial overlapping length on the vehicle landing performance is carried out. The results show that each parameter has different influence on the landing performance, and a reasonable selection of these parameters accordingly enables a higher landing performance.

Chaos phenomenon and stability analysis of RU-RPR parallel mechanism with clearance and friction

The chaos phenomenon often exists in the dynamics system of the mechanism with clearance and friction, which has obvious effect on the stability of the mechanism, then it is worthy of attention for identifying the relationship between the friction coefficient and the stability of the mechanism. Two rotational degrees of freedom decoupled parallel mechanism RU-RPR is taken as the research object. Considering the clearance existing in the revolute pair, Lankarani–Nikravesh contact force model is used to calculate the normal contact force, and the Coulomb friction force model is used to calculate the tangential contact force. The dynamics model is established using Newton–Euler equations, and the Baumgarte stabilization method is used to keep the stability of the numerical analysis. Then, the equations are solved using the fourth adaptive Runge–Kutta method, and the effect of the revolute pair’s clearance on the dynamic behavior is analyzed. Poincare mapping is plotted, and the bifurcation diagrams are analyzed with varying the friction coefficient corresponding to different values of clearance size. The research contents possess a certain theoretical guidance significance and practical application value on the analysis of the chaotic motion and its stability in the dynamics of the parallel mechanism.

A novel technique for modeling friction behavior in knitted fabric simulation

PurposeFabric-object friction force is a fundamental factor in cloth simulation. A large number of parameters influence the frictional properties of fabrics such as fabric structure, yarn structure, and inherent properties of component fibers. The purpose of this paper is to propose a novel technique for modeling fabric-object friction force in knitted fabric simulation based on the mass spring model.Design/methodology/approachIn this technique, unlike other studies, distribution of friction coefficient over the fabric surface is not uniform and depends on the fabric structure. The main reason for considering non-uniform distribution is that in various segments of fabric, contact percent of fabric-object is different.FindingsThe proposed technique and common methods based on friction coefficient uniform distribution are used to simulate the frictional behavior of knitted fabrics. The results show that simulation error values for proposed technique and common methods are 2.7 and 9.4 percent as compared with the experimental result, respectively.Originality/valueIn the existing methods of the friction force modeling, the friction coefficient of fabric is assumed uniform. But this assumption is not correct because fabric does not have an isotropic structure. Thus in this study, the friction coefficient distribution is considered based on fabric structure to achieve more of realistic simulations.

Dynamic and motion consistency analysis for a planar parallel mechanism with revolute dry clearance joints

The aim of the research was to introduce a methodology for dynamic response and motion consistency research on multibody system with multiple revolute clearance joints. An improved impact force model and a modified friction force model were introduced to evaluate the effects of impact and friction in clearance joints. A planar parallel mechanism which has two clearance joints in the left wing and the right wing was also used as an example. From the results based on different conditions, clearance has slight influence on the angular displacement and angular velocity, but obvious effect on angular acceleration. And with same clearance values of left wing and right wing, the motion consistency of the parallel mechanism is very good, which means the dynamic response of two wings is almost symmetrical. When the two clearance joints have different clearance values, the motion consistency and relative error between two wings are much obvious, especially the angular acceleration.

A Study on the Dynamics of Spatial Mechanisms With Frictional Spherical Clearance Joints

An investigation on the dynamic modeling and analysis of spatial mechanisms with spherical clearance joints including friction is presented. For this purpose, the ball and the socket, which compose a spherical joint, are modeled as two individual colliding components. The normal contact-impact forces that develop at the spherical clearance joint are determined by using a continuous force model. A continuous analysis approach is used here with a Hertzian-based contact force model, which includes a dissipative term representing the energy dissipation during the contact process. The pseudopenetration that occurs between the potential contact points of the ball and the socket surface, as well as the indentation rate play a crucial role in the evaluation of the normal contact forces. In addition, several different friction force models based on the Coulomb's law are revisited in this work. The friction models utilized here can accommodate the various friction regimens and phenomena that take place at the contact interface between the ball and the socket. Both the normal and tangential contact forces are evaluated and included into the systems' dynamics equation of motion, developed under the framework of multibody systems formulations. A spatial four-bar mechanism, which includes a spherical joint with clearance, is used as an application example to examine and quantify the effects of various friction force models, clearance sizes, and the friction coefficients.

Effect of frictional heat generation on the temperature distribution in roller linear motion rail surface

The temperature distribution in roller Linear motion (LM) rail surface heated with moving frictional heat source was investigated experimentally and numerically. The operating conditions which had not been regarded by previous research, such as the type of the LM guide and operating temperature, were taken into account for improving the previous model of friction force. Frictional heat generation model and heat partitioning coefficient were proposed to calculate the heat transferred to the LM rail. The numerical solutions were calculated in combining a heat conduction equation and the rate of frictional heat flowing into the rail. Frictional heat generation model and heat partitioning coefficient were verified by comparing experimental and numerical results. Simulation results showed that smaller LM block size or higher velocity leads to the higher temperature distribution in the rail surface. Results also indicated that larger motion stroke results in a lower and wider temperature distribution in the rail surface.

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.

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.

Experimental evaluation of cooling performance by friction coefficient and specific friction energy in nanofluid minimum quantity lubrication grinding with different types of vegetable oil

In accordance with the lubricating performance of nanofluid minimum quantity lubrication (N-MQL) grinding with different vegetable oils as the base oil in previous research, cooling performance was explored with a new method. Friction coefficient, specific friction energy, total heat flow density, and grinding peak temperature were used as evaluation parameters. The influence of the physical properties (viscosity, surface tension) of vegetable oils on the cooling effect was analyzed comprehensively. For the new method, a new ploughing force model and a friction force model were established, and cutting force and ploughing force were calculated theoretically. Afterward, friction force was obtained according to the theoretical model and experimental results and was used to calculate the evaluation parameters. The vegetable oil nanofluids showed better cooling performance than mineral oil because of their lubrication-favorable fatty acid molecules. Furthermore, the mechanism of the effect of nanofluid viscosity and surface tension on cooling performance was explored. Vegetable oil with a low viscosity and surface tension showed good cooling performance and that with a high viscosity and surface tension showed good lubrication performance. As a result, palm oil nanofluid with a high viscosity and surface tension achieved the lowest friction coefficient (0.258), specific friction energy (27.09 J/mm3), and grinding peak temperature (123.8 °C) and exhibited better grinding performance than the others.

A survey and comparison of several friction force models for dynamic analysis of multibody mechanical systems

This study is aimed at examining and comparing several friction force models dealing with different friction phenomena in the context of multibody system dynamics. For this purpose, a comprehensive review of present literature in this field of investigation is first presented. In this process, the main aspects related to friction are discussed, with particular emphasis on the pure dry sliding friction, stick–slip effect, viscous friction and Stribeck effect. In a simple and general way, the friction force models can be classified into two main groups, namely the static friction approaches and the dynamic friction models. The former group mainly describes the steady-state behavior of friction force, while the latter allows capturing more properties by using extra state variables. In the present study, a total of 21 different friction force models are described and their fundamental physical and computational characteristics are discussed and compared in details. The application of those friction models in multibody system dynamic modeling and simulation is then investigated. Two multibody mechanical systems are utilized as demonstrative application examples with the purpose of illustrating the influence of the various frictional approaches on the dynamic response of the systems. From the results obtained, it can be stated that both the choice of the friction force model and friction parameters involved can significantly affect the simulated/modeled dynamic response of mechanical systems with friction.

A smooth model of the resultant friction force on a plane contact area

A class of smooth approximations of the total friction force occurring on a plane finite contact surface is presented. It is assumed that the classical Coulomb friction law is valid on any infinitesimal element of the contact region. The models describe the stick phase, the fully developed sliding and the transition between these two modes. They take into account different values of static and dynamic friction coefficients. The models are applied in simulation of a dynamical system performing translational and rotational stick-slip oscillations, and then they are verified by comparison with the corresponding results in which an event-driven discontinuous model of friction is used.

Simulation of material plastic flow driven by non-uniform friction force during friction stir welding and related defect prediction

Material flow during welding is an important factor that affects the quality of friction stir welding (FSW) joints. In this study, a new welding tool/work piece contact model is proposed to simulate material flow near the FSW tool. The material around the tool flows under the driving force of friction non-uniformly distributed on the interface. Friction force is calculated based on modified Coulomb friction law in this model. Wormhole defects under various welding parameters are graphically predicted by the distribution of tracing particles added in numerical models. Five groups of FSW experiments were conducted to obtain temperature and joint morphology results. Simulation results, including temperature and wormhole defects prediction, corresponded with the experimental results. Further analyses imply that under the process parameters selected in this study, an area with very low friction force occurred behind the tool pin. When the material in front of the tool pin moved to this area from the retreating side, the material speed significantly decreased due to the insufficient driving force, and it became difficult for the material to move to the advancing side along the circular path. The study reveals that the non-uniform friction force model provides a potential tool for predicting FSW defects.

Physics-Based Flexible Tire Model Integrated With LuGre Tire Friction for Transient Braking and Cornering Analysis

In transient vehicle maneuvers, structural tire deformation due to the large load transfer causes abrupt change in normal contact pressure and slip distribution over the contact patch, and it has a dominant effect on characterizing the transient braking and cornering forces including the history-dependent friction-induced hysteresis effect. To account for the dynamic coupling of structural tire deformations and the transient tire friction behavior, a physics-based flexible tire model is developed using the laminated composite shell element based on the absolute nodal coordinate formulation and the distributed parameter LuGre tire friction model. In particular, a numerical procedure to integrate the distributed parameter LuGre tire friction model into the finite-element based spatial flexible tire model is proposed. To this end, the spatially discretized form of the LuGre tire friction model is derived and integrated into the finite-element tire model such that change in the normal contact pressure and slip distributions over the contact patch predicted by the deformable tire model enters into the spatially discretized LuGre tire friction model to predict the transient shear contact stress distribution. By doing so, the structural tire deformation and the LuGre tire friction force model are dynamically coupled in the final form of the equations, and these equations are integrated simultaneously forward in time at every time step. The tire model developed is experimentally validated and several numerical examples for hard braking and cornering simulation are presented to demonstrate capabilities of the physics-based flexible tire model developed in this study.

On some approximations of the resultant contact forces and their applications in rigid body dynamics

The work presents the possible applications and effectiveness of certain class of models of the resultant friction force and rolling resistance. The friction models are based on the integral model constructed under assumption of fully developed sliding on the plane contact area of general shape and any pressure distribution. Then the integral model of friction force and moment are approximated based on Padé approximants and their generalizations. These models are expected to be computationally effective in numerical simulations of rigid bodies with frictional contacts, such like billiard balls, Thompson top, the wobble stone and many others. In the present work two different examples of application of the developed contact models are presented and tested: a) a billiard ball rolling and sliding on the plane horizontal table; b) a full ellipsoid of revolution in contact with plane and horizontal base.

Cutting force analysis to estimate the friction force in linear guideways of CNC machine

Linear guideways are widely applied in advanced machinery industries worldwide for different types of CNC machine (e.g., turning, milling, grinding, and gantry). All of these machines require accuracy and precision in the machining operations to manufacture quality products. The cutting operation in product manufacturing occurs with the displacement of machine tables on linear guideways. For this reason, linear guideways are significant parts and have sensitive locations in CNC machines to yield precision and accuracy. Friction is a major factor of deformation in guideways and non-smooth motion that prevents superior accuracy and precision in machine operations. Moreover, the frictional behavior in linear guideways is one of the most crucial challenges for CNC machining, such that between two parts of friction and temperature stimulus there will be stick-slip motion, wear and corrosion of the parts. Thus, manufacturers are interested in these machines, particularly to facilitate this process with an actual lubrication system. Hence, friction force estimation and modeling in CNC machine guideways is used to overcome these problems by controlling the lubrication operation.In this research work, the cutting force components including, longitudinal force (FL), radial force (Fr) and tangential force (Ft) are measured during cutting process. These cutting force values are corresponding to different cutting conditions includes, spindle speed, depth of cut, and feed rate. The cutting force components and the weight of the moving parts are analyzed and transferred to the CNC machine guideways. The friction force on linear guideways of machine tools is modeled based on the analyzed and transferred force components on the guideways during cutting. The static and kinetic coefficient of friction are measured experimentally in dry lubrication condition hence the friction force components can be obtained. The friction force are estimated using the identified coefficient of friction.

Review and comparison of dry friction force models

Friction force models play a fundamental role for simulation of mechanical systems. Their choice affects the matching of numerical results with physically observed behavior. Friction is a complex phenomenon depending on many physical parameters and working conditions, and none of the available models can claim general validity. This paper focuses the attention on well-known friction models and offers a review and comparison based on numerical efficiency. However, it should be acknowledged that each model has its own distinctive pros and cons. Suitability of the model depends on physical and operating conditions. Features such as the capability to replicate stiction, Stribeck effect, and pre-sliding displacement are taken into account when selecting a friction formulation. For mechanical systems, the computational efficiency of the algorithm is a critical issue when a fast and responsive dynamic computation is required. This paper reports and compares eight widespread engineering friction force models. These are divided into two main categories: those based on the Coulomb approach and those established on the bristle analogy. The numerical performances and differences of each model have been monitored and compared. Three test cases are discussed: the Rabinowicz test and other two test problems casted for this occurrence.

Stochastic modeling of friction force and vibration analysis of a mechanical system using the model

The squeal noise generated from a disk brake or chatter occurred in a machine tool primarily results from friction-induced vibration. Since friction-induced vibration is usually accompanied by abrasion and lifespan reduction of mechanical parts, it is necessary to develop a reliable analysis model by which friction-induced vibration phenomena can be accurately analyzed. The original Coulomb’s friction model or the modified Coulomb friction model employed in most commercial programs employs deterministic friction coefficients. However, observing friction phenomena between two contact surfaces, one may observe that friction coefficients keep changing due to the unevenness of contact surface, temperature, lubrication and humidity. Therefore, in this study, friction coefficients are modeled as random parameters that keep changing during the motion of a mechanical system undergoing friction force. The integrity of the proposed stochastic friction model was validated by comparing the analysis results obtained by the proposed model with experimental results.

Haptic Interfaces for Compensating Dynamics of Rescue Walking Robots

This paper presents a Neural Network approach to compensate dynamic terms, friction force in particular, of a rescue walking robot used in haptic interfaces. The impedance control through dynamic compensation of the friction force is studied, followed by the implementation of neural intelligent networks in the feed-forward loop in order to eliminate the corresponding terms in the dynamics, friction force in particular. The friction force model is analyzed using a general compensation method after which a trained Multi-Layer Neural Network is introduced in order to obtain an accurate friction model so that the movement of the walking robot feels free and unconstraint.

A Force Sensorless Method for CFRP/Ti Stack Interface Detection during Robotic Orbital Drilling Operations

Drilling carbon fiber reinforced plastics and titanium (CFRP/Ti) stacks is one of the most important activities in aircraft assembly. It is favorable to use different drilling parameters for each layer due to their dissimilar machining properties. However, large aircraft parts with changing profiles lead to variation of thickness along the profiles, which makes it challenging to adapt the cutting parameters for different materials being drilled. This paper proposes a force sensorless method based on cutting force observer for monitoring the thrust force and identifying the drilling material during the drilling process. The cutting force observer, which is the combination of an adaptive disturbance observer and friction force model, is used to estimate the thrust force. An in-process algorithm is developed to monitor the variation of the thrust force for detecting the stack interface between the CFRP and titanium materials. Robotic orbital drilling experiments have been conducted on CFRP/Ti stacks. The estimate error of the cutting force observer was less than 13%, and the stack interface was detected in 0.25 s (or 0.05 mm) before or after the tool transited it. The results show that the proposed method can successfully detect the CFRP/Ti stack interface for the cutting parameters adaptation.