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2000 | Buch

Structure of Machines and Mechanisms Kapitel lesen Erstes Kapitel lesen

Advanced Theory of Mechanisms and Machines

verfasst von: M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch

Verlag: Springer Berlin Heidelberg

Buchreihe : Foundations of Engineering Mechanics

Enthalten in: Professional Book Archive

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Über dieses Buch

This book is based on a lecture course delivered by the authors over a period of many years to the students in mechanics at the St. Petersburg State Technical University (the former Leningrad Polytechnic Institute). The material differs from numerous traditional text books on Theory of Machines and Mechanisms through a more profound elaboration of the methods of structural, geometric, kinematic and dynamic analysis of mechanisms and machines, consisting in both the development of well-known methods and the creation of new ones that take into account the needs of modem machine building and the potential of modem computers. The structural analysis of mechanisms is based on a new definition of structural group which makes it possible to consider closed structures that cannot be reduced to linkages of Assur groups. The methods of geometric analysis are adapted to the analysis of planar and spatial mechanisms with closed structure and several degrees of movability. Considerable attention is devoted to the problems of con­ figuration multiplicity of a mechanism with given input coordinates as well as to the problems of distinguishing and removing singular positions, which is of great importance for the design of robot systems. These problems are also reflected in the description of the methods of kinematic analysis employed for the investi­ gation of both open ("tree"-type) structures and closed mechanisms.

Inhaltsverzeichnis

Frontmatter
1. Structure of Machines and Mechanisms
Abstract
Modern industrial production is reduced in the end to the execution of a great number of diverse working processes. Most processes are associated with treatment and transformation of initial raw materials into half- or fully finished products; such working processes are referred to as technological. Technological processes involve transportation of materials to the place of utilization as well as energy processes, i.e. generation and transformation of energy in forms most convenient for the respective proccess. Also, information processes, i.e. transmission and transformation of information are of great importance in modern production, ensuring execution of operations associated with control and organization of production.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
2. Geometric Analysis of Mechanisms
Abstract
The subject of geometric analysis is to determine the position functions of a mechanism, i.e. relationships between output mechanism coordinates x1, x2,..., x m determining link positions and the input mechanism coordinates q1, q2,.., q n . For mechanisms with n degrees of movability these functions are written in the form
$$ {x_s} = {\Pi _s}({q_1},{q_2},...,{q_n})\;(s = 1,2,...,m) $$
(2.1)
. The determination of these relationships constitutes the direct problem of geometric analysis. Having solved the direct problem it is possible to determine for given time functions of input varibales q k (t)(k = 1,2,...,n) the output coordinates as functions of time
$$ {x_s}(t) = {\Pi _s}[{q_1}(t),{q_2}(t),...,{q_n}(t)]\;(s = 1,2,...,m) $$
(2.2)
. For a mechanism with one degree of movability, the position functions are functions of a single variable q:
$$ {x_s} = {\Pi _s}(q)\;(s = 1,2,...,m) $$
(2.3)
.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
3. Kinematic and Parametric Analysis of Mechanisms
Abstract
The goal of kinematic analysis is to determine velocities and accelerations of mechanism points, as well as angular velocities and accelerations of links. In addition, analogously to the geometric analysis, direct and inverse problems are solved.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
4. Determination of Forces Acting in Mechanisms
Abstract
Mechanisms are used not only for producing program motions but also for transmitting forces, necessary, both, for performing working processes and for overcoming the inertia of moving links. For this reason the kinematic and geometric investigation must be complemented by the analysis of forces in the process of mechanism design.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
5. Friction in Mechanisms
Abstract
At kinematic pairs of real mechanisms friction forces are acting. In many cases these forces have a major influence on the mechanism motion and must be taken into account in the force analysis.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
6. Equations of Motion for a Mechanism with Rigid Links
Abstract
Until now, it was presumed that the motion law of a mechanism is known: it was assumed that the law is the program law necessary for the execution of a working proccess. In a real machine the actual motion differs from the program motion. This difference is primarily related to the properties of the engine, setting the machine in motion and generating driving forces applied to input links. The output velocity of the engine depends on the magnitude of the generalized driving force, and this must be taken into account when designing a machine assembly. It is necessary to integrate the system of differential equations of the mechanical system together with the engine characteristic. Usually, differential equations of motion for a mechanism are in the form of Lagrange’s equations of the second kind.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
7. Dynamic Characteristics of Mechanisms with Rigid Links
Abstract
For an assessment of the quality of a mechanism, it is necessary to proceed from the acting forces and from the constraint reactions obtained in the force analysis, to some general dynamic criteria which reflect the most important properties of a mechanism in the most typical dynamic regimes. In this chapter we will consider methods of defining dynamics characteristics as well as methods of improving the qualities of a mechanism through a modification of its parameters and through the introduction of certain complementary devices.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
8. Dynamics of Cycle Machines with Rigid Links
Abstract
For the solution of problems of machine dynamics we usually use the simplest dynamic engine models desplaying the dependencies among the following time laws: The law u(t) of the input parameter (control) of the engine, the law q(t) of the generalized coordinate and the law Q(t) of the generalized driving force (see Sect. 1.2). The mathematical relationships describing these dependencies are called mechanical characteristics of engines. Comparatively rarely, it is necessary to refer to more complex models which take into account the dynamics of internal physical processes in engines. In the present course such models will not be considered.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
9. Dynamics of Mechanisms with Elastic Links
Abstract
We will call mechanism with elastic links or simply elastic mechanism a dynamic model of a real mechanism obtained under the assumption that some constructive elements of its links and kinematic pairs are deformable. From this definition it follows that mechanisms with elastic links can be obtained from the corresponding rigid mechnisms, if in the latter some rigid constraints are replaced by deformable ones. Let us illustrate this with concrete examples.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
10. Vibration of Machines with Elastic Transmission Mechanisms
Abstract
In mechanisms with rigid links motion is accompanied, as is well-known, by the generation of dissipative forces acting at kinematic pairs. Earlier the influence of forces of Coulomb friction on the motion of rigid mechanisms and on the efficiency mechanism has been investigated. In mechanisms with elastic links dissipative forces are also caused by deformations of elastic elements
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
11. Vibration of a Machine on an Elastic Base. Vibration Isolation of Machines
Abstract
No base on which a machine is being mounted is perfectly rigid. Time-varying forces caused by unbalanced mechanisms which act on the machine body lead to deformations of the base or of elements connecting the machine body with the base. Also, vibrations of the machine body itself occur which may lead to perturbations of the working process; so, e.g., the vibration of the body of a metalcutting machine tool may deteriorate the accuracy of the blank processing.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
12. Elements of Dynamics of Machines with Program Control
Abstract
In modern machine building two methods are applied for designing program motions of working organs of a machine necessary for the fulfillment of specified working processes. The first method which is widely used for single-engine cycle machines consists in feeding the engine input with an input signal ensuring a nearly uniform rotation at the output of a rotor engine or a periodically reciprocating motion (in a linear engine). The transformation of these simplest motions into desired program motions of working organs is carried out by actuating mechanisms (lever-, cam-, gear- and other ones) which have, as a rule, nonlinear position functions. One might say that programming mechanisms are applied in such machines.
M. Z. Kolovsky, A. N. Evgrafov, Yu. A. Semenov, A. V. Slousch
Backmatter
Metadaten
Titel
Advanced Theory of Mechanisms and Machines
verfasst von
M. Z. Kolovsky
A. N. Evgrafov
Yu. A. Semenov
A. V. Slousch
Copyright-Jahr
2000
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-540-46516-4
Print ISBN
978-3-642-53672-4
DOI
https://doi.org/10.1007/978-3-540-46516-4