86,814 research outputs found
Enhanced brush model for the mechanics of power transmission in flat belt drives under steady–state conditions: Effect of belt elasticity
No full textThe present paper is an extension of a previously published paper by the authors, where the “brush” model was adopted for the contact stresses between the belt and pulleys. In this paper, the axial stiffness of the belt is introduced, while in previous work, particularly suited for belt with stiff reinforcement fibers, the belt was assumed to be inextensible. The complete set of equations is derived in steady state conditions and the relationship between belt tension and belt speed is introduced based on the continuity condition. The belt tension can be obtained by solving a second order differential equation, for which a closed form solution is given. A numerical procedure is, however, necessary for determining the solution of a given transmission with assigned rotational speed at the driving pulley and resistant moment at the driven pulley. It is shown how the contact angle at which stick–slip phenomenon may occur is influenced by the belt stiffness and the way the transmission effiency is reduced. Allowing to analyze the mechanics of flat belt transmission, the model can be considered a useful tool for the designer
“Brush model” for the analysis of flat belt transmissions in steady-state conditions
Get PDFIn the present work a novel mathematical model for the analysis of the contact actions between belt and pulleys, particularly suited for flat reinforced rubber belt, is presented. The model considers the tension member, composed of the reinforcement fibers, inextensible, and the rubber matrix, which is subjected to tangential stress, as a continuum bed of elastically deformable bristles, fixed to the tension member on one side and in contact with the pulley on the other side. The deformation of the matrix is inversely proportional to the bending stiffness of the bristles, while friction conditions determine the local adhesion/sliding behavior between belt and pulleys. The proposed model can give a detailed description of the contact conditions along the whole contact arc and is able to describe the stick–slip phenomenon which has been experimentally observed by some authors. The model assesses also the power losses due to the contact stresses and to the elastic deformation of the matrix. The results of the model are discussed in comparison with results from classical models, Grashof and Firbank models, available in the technical literature
Analysis of belt transmissions capabilities using the brush model
Get PDFThe mechanics of power transmission is usually modeled by two different theories: the creep theory and the shear theory. Recently, the authors introduced an alternative theory based on the brush model, which allows to compute the tangential stress distribution along the winding arc of pulleys. The brush model is able to predict the speed loss along the driving and driven pulley as a function of the transmission parameters (e.g. pre-load, friction, pulley radii etc.) and the operating parameters (i.e. angular speed and resistant torque). In addition, the energy efficiency of the system is obtained by knowing the speed loss and the energy dissipation; this contribution can be subdivided into energy loss due to friction and energy loss due to the non-recoverable elastic deformation of the bristle.
In the present paper, using the previously developed model, a sensitivity analysis aimed at mapping the transmission capabilities as a function of geometry and operating parameters is proposed. These results, given as look-up table (or contour plot), are very important in mechanical systems simulation (e.g. real-time systems, hardware in the loop systems) since they allow to introduce the phenomenological behavior of the pulley-belt transmission without introducing complex models in the simulation
Validation of the brush model for the analysis of flat belt transmissions in steady-state conditions by finite element simulation
No full textIn this paper a finite element (FE) model for the analysis of the contact stresses in flat belt transmissions was developed, with the intent of comparing the numerical with the theoretical results of the brush model and those of the classical Euler–Grashof (creep) model. The FE model consists of two pulleys and a belt composed of a thin layer of inextensible reinforcement fibers and a rubber matrix in contact with the pulley. The analysis is performed incrementally, under quasi-static conditions; as a consequence, any inertia effect is not accounted for. In the paper, the capabilities of the analyzed models are discussed. The brush model is generally better correlated with the FE results, both in terms of tangential stress along the winding arc and belt tension and it is capable of estimating the power losses due to friction with low computational and time effort. In addition, the effect of the belt thickness on the tangential stress at the entrance and the exit from the pulley, which are generally neglected by simplified model, are highlighted by the FE analysis
Modello a spazzola per le azioni di contatto tra cinghia e puleggia, per trasmissioni con cinghie piatte in regime stazionario
No full textAnalytical Derivation and Analysis of Vertical and Lateral Installation Ratios for Swing Axle, McPherson and Double Wishbone Suspension Architectures
No full textIn the context of suspension design, the installation ratio (or motion ratio) is a parameter that relates wheel movement with spring deflection, quite an important kinematic property of a suspension. Yet, no study in the literature provides a clear relationship between the installation ratio and the geometrical features of a suspension. This paper employs rigid body kinematics and appropriate geometrical schematics to fill such a gap. Analytical expressions of the installation ratio are derived for three suspension layouts: swing axle, McPherson, double wishbone. Key concepts such as instant center, roll center and camber gain are harnessed to provide insightful analyses for relevant case studies of suspension passenger cars. Among the key results, the typical assumption of a McPherson installation ratio close to 1 is supported by a formal demonstration, and the new concept of “lateral” installation ratio is introduced which, alongside the classical “vertical” installation ratio, further characterizes suspension motion. Numerical results obtained through a multibody software support the findings of this paper. In conclusion, this study provides valuable insights for suspension design engineers
Simulation of the Vibratory Behavior of Slender Shafts Subject to Transverse Loads Moving in the Axial Direction
No full textIn various machines of the manufacturing industry, and in particular in paper converting machinery, there are shafts operating under conditions similar to that of a slender beam subjected to a transverse load moving in the axial direction. This condition can lead to vibrations and consequent deterioration of the machine performance and of the product quality. The problem has been theoretically studied in the literature since the 1990s. While shaft mass and stiffness are universally considered among the most influential parameters on its vibratory behavior, less obvious and not investigated in the literature is the influence of the spatial interval between two successive loads, an aspect that should be considered in the shaft design phase. In fact, if that is less than the length of the shaft, i.e., if there is more than one transverse load on the shaft at a given time, the vibration level may decrease with respect to the single-load configuration. This work describes the development of a mathematical model of a slender shaft hinged at its ends, representing the rotor of a paper roll perforating unit, with the SW Mathematica. The effect of a load moving axially at a given speed followed by similar loads after given spatial intervals was simulated investigating the influence of speed and load interval on shaft vibrations and resonance. The results showed how reducing the load interval can lead to a reduction of the shaft vibration which is a useful indication on possible design corrective actions
Sviluppo mediante approccio FEM-multibody di un sistema sospensivo per il trasporto su strada del criomodulo SSR1
No full textMulti-body simulation of a rope-driven automated people mover
Get PDF In this paper, a multibody model of the automated people mover, PisaMover, is presented. PisaMover is a rope-driven small train, composed of a few cabins, which makes use of train-inspired bogies. The aim of the model was to support the design of the architecture of the suspensions and to select the proper characteristics of the elastic and damping elements in order to fulfill comfort needs of passengers and to resolve the constraints related to the layout of the vehicle and the guide-ways. For this purpose, attention was especially focussed on the definition of the railway path and the modeling of the forces of the supporting and guidance wheels. A simplified model of the rope was implemented, which neglects the rope elasticity and computes the rope force direction taking account of the different positions of the sheaves along the path. The multibody simulation allowed to select the most appropriate suspension system and to properly define the elastic and damping characteristics of the shock absorbers, with respect to the technical constraints. A modal analysis was performed, and several dynamic on-track simulations were carried out to infer the effect of dampers’ design on the comfort of passengers. Within the validity of the simplifying assumptions, the multibody simulation also allowed to obtain a fairly good estimate of the loads necessary for the design of the main structural components. </jats:p
Analytical Derivation and Analysis of Vertical and Lateral Installation Ratios for Swing Axle, McPherson and Double Wishbone Suspension Architectures
Get PDFIn the context of suspension design, the installation ratio (or motion ratio) is a parameter that relates wheel movement with spring deflection, quite an important kinematic property of a suspension. Yet, no study in the literature provides a clear relationship between the installation ratio and the geometrical features of a suspension. This paper employs rigid body kinematics and appropriate geometrical schematics to fill such a gap. Analytical expressions of the installation ratio are derived for three suspension layouts: swing axle, McPherson, double wishbone. Key concepts such as instant center, roll center and camber gain are harnessed to provide insightful analyses for relevant case studies of suspension passenger cars. Among the key results, the typical assumption of a McPherson installation ratio close to 1 is supported by a formal demonstration, and the new concept of “lateral” installation ratio is introduced which, alongside the classical “vertical” installation ratio, further characterizes suspension motion. Numerical results obtained through a multibody software support the findings of this paper. In conclusion, this study provides valuable insights for suspension design engineers
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