## FUNDAMENTALS OF KINEMATICS AND DYNAMICS OF MACHINES AND MECHANISMS

## BY OLEG VINOGRADOV

## FREE DOWNLOAD PDF

**CONTENTS**

**Introduction****Kinematic Analysis of Mechanisms****Force Analysis of Mechanisms****Cams****Gears****Introduction to Linear Vibrations**

**INTRODUCTION TO THIS BOOK :**

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This subject is a continuation of statics and dynamics, which is taken by students

in their freshman or sophomore years. In kinematics and dynamics of machines and

mechanisms, however, the emphasis shifts from studying general concepts with

illustrative examples to developing methods and performing analyses of real designs.

This shift in emphasis is important, since it entails dealing with complex objects

and utilizing different tools to analyze these objects.

The objective of kinematics is to develop various means of transforming motion

to achieve a specific kind needed in applications. For example, an object is to be

moved from point A to point B along some path. The first question in solving this

problem is usually: What kind of a mechanism (if any) can be used to perform this

function? And the second question is: How does one design such a mechanism?

The objective of dynamics is analysis of the behavior of a given machine or

mechanism when subjected to dynamic forces. For the above example, when the

mechanism is already known, then external forces are applied and its motion is

studied. The determination of forces induced in machine components by the motion

is part of this analysis.

As a subject, the kinematics and dynamics of machines and mechanisms is

disconnected from other subjects (except statics and dynamics) in the Mechanical

Engineering curriculum. This absence of links to other subjects may create the false

impression that there are no constraints, apart from the kinematic ones, imposed on

the design of mechanisms. Look again at the problem of moving an object from A

to B. In designing a mechanism, the size, shape, and weight of the object all constitute

input into the design process. All of these will affect the size of the mechanism.

There are other considerations as well, such as, for example, what the allowable

speed of approaching point B should be. The outcome of this inquiry may affect

either the configuration or the type of the mechanism. Within the subject of kinematics

and dynamics of machines and mechanisms such requirements cannot be

justifiably formulated; they can, however, be posed as a learning exercise.

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Force Analysis of

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Mechanisms

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INTRODUCTION

The design of mechanisms and their components requires information about forces

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acting on these components. Some mechanisms are designed to perform a specific

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kinematic function (like the windshield wiper mechanism, Figure 1.4), others to

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transfer energy (like the internal combustion engine). However, in any mechanism,

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identification of forces is needed to determine the proper dimensions of components.

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The power supplied to the input link flows through the mechanism to the output

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link. Associated with this power flow is a force flow. The objective of the force

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analysis of mechanisms is to find the transformation of forces from the input to the

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output links. This transformation of forces depends on the position of the mechanism;

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in other words, it is a function of time. Thus, it is important to find out how these

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forces change during one cycle in order to find their maxima.

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One should differentiate between two types of forces: external and internal. The

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former are forces that are applied to the links from external (with respect to the

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mechanism) sources — driving forces, resistance forces — whereas the latter are

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forces acting between the joints (they are called constraint or reaction forces).

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The motion of a mechanism is caused by the known external forces, and can be f

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ound by formulating and solving the differential equation describing the dynamic

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equilibrium of the mechanism at any moment in time. This approach to motion

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analysis is called direct dynamics. An alternative approach is to assume that the

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motion is known (in other words, the motion of the input link is given as a function

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of time). Then, as a result of kinematic analysis, the accelerations of all links are

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known, and thus the inertial forces associated with these links. These inertial forces

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can be treated as known external forces, and the force analysis is then reduced to

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solving equilibrium equations for the mechanism at any given position. This

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approach to force analysis is called inverse dynamics. It is important to keep in mind

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that inverse dynamics is based on the assumption of known motion, whereas in fact

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such motion can be found only from direct dynamics analysis. However, in many

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situations the much simpler inverse dynamics approach is sufficient as a first approximation

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This approach is considered in this book.

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To summarize, it is assumed here that the forces acting on the input link are

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given as a function of time (or link position) and the inertial (dynamic) forces are

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also known as a result of kinematic analysis of motion. The objective of force analysis

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then is to find the internal and resistance forces. The method of solution is to perform

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static analysis of a mechanism in a number of fixed positions over the region of

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input link motion.

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DOWNLOAD LINK : Fundamentals of Kinematics and Dynamics of Machines and Mechanisms www.MechanicaLibrary.com

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