Theory of Machines and Mechanisms 3rd Edition
This book is intended to cover that field of engineering theory, analysis, design, and practice that is generally described as mechanisms and kinematics and dynamics of machines. While this text is written primarily for students of engineering, there is much material that can be of value to practicing engineers. After all, a good engineer knows that he or she must remain a student throughout their entire professional career.
The continued tremendous growth of knowledge, including the areas of kinematics and dynamics of machinery, over the past 50 years has resulted in great pressure on the engineering curricula of many schools for the substitution of “modern” subjects for those perceived as weaker or outdated. At some schools, depending on the faculty, this has meant that kinematics and dynamics of machines could only be made available as an elective topic for specialized study by a small number of students; at others it remained a required subject for all mechanical engineering students. At other schools, it was required to take on more design emphasis at the expense of depth in analysis. In all, the times have produced a need for a textbook that satisfies the requirements of new and changing course structures.
Much of the new knowledge developed over this period exists in a large variety of technical papers, each couched in its own singular language and nomenclature and each requiring additional background for its comprehension. The individual contributions being published might be used to strengthen the engineering courses if first the necessary foundation were provided and a common notation and nomenclature were established. These new developments could then be integrated into existing courses so as to provide a logical, modern, and comprehensive whole. To provide the background that will allow such an integration is the purpose of this book.
To develop a broad and basic comprehension, all the methods of analysis and development common to the literature of the field are employed. We have used graphical methods of analysis and synthesis extensively throughout the book because the authors are firmly of the opinion that graphical computation provides visual feedback that enhances the student’s understanding of the basic nature of and interplay between the equations involved. Therefore, in this book, graphic methods are presented as one possible solution technique for vector equations defined by the fundamental laws of mechanics, rather than as mysterious graphical “tricks” to be learned by rote and applied blindly. In addition, although graphic techniques may be lacking in accuracy, they can be performed quickly and, even though inaccurate, sketches can often provide reasonable estimates of a solution or can be used to check the results of analytic or numeric solution techniques.
We also use conventional methods of vector analysis throughout the book, both in deriving and presenting the governing equations and in their solution. Raven’s methods using complex algebra for the solution of two-dimensional vector equations are ployed so frequently in the literature, and also because they are so easy to program for computer evaluation. In the chapters dealing with three-dimensional kinematics and robotics, we briefly present an introduction to Denavit and Hartenberg’s methods using transformation matrices.
With certain exceptions, we have endeavored to use U.S. Customary units and SI units in about equal proportions throughout the book. One of the dilemmas that all writers on the subject of this book have faced is how to distinguish between the motions of two different points of the same moving body and the motions of coincident points of two different moving bodies. In other texts it has been customary to describe both of these as “relative motion”; but because they are two distinct situations and are described by different equations, this causes the student difficulty in distinguishing between them. We believe that we have greatly relieved this problem by the introduction of the terms motion difference and apparent motion and two different notations for the two cases. Thus, for example, the book uses the two terms, velocity difference and apparent velocity, instead of the term “relative velocity,” which will not be found when speaking rigorously. This approach is introduced beginning with the concepts of position and displacement, used extensively in the chapter on velocity, and brought to fulfillment in the chapter on accelerations where the Coriolis component always arises in, and only in, the apparent acceleration equation.
Another feature, new with the third edition, is the presentation of kinematic coefficients, which are derivatives of various motion variables with respect to the input motion rather than with respect to tirr.e. The authors believe that these provide several new and important advantages, among which are the following: (1) They clarify for the student those parts of a motion problem which are kinematic (geometric) in their nature, and they clearly separate them from those that are dynamic or speed-dependent. (2) They help to integrate different types of mechanical systems and their analysis, such as gears, cams, and linkages, which might not otherwise seem similar.
Access to personal computers and programmable calculators is now commonplace and is of considerable importance to the material of this book. Yet engineering educators have told us very forcibly that they do not want computer programs included in the text. They prefer to write their own programs and they expect their students to do so too. Having programmed almost all the material in the book many times, we also understand that the book should not become obsolete with changes in computers or programming languages.
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