Jnl. Mechanisms Volume 4, pp.181-185/Pergamon Press 1 969/Printed in Great Britain

Book Reviews

S a m u e l M o l i a n : The Design of Cam Mechanisms and Linkages

Amer i can Elsevier, New York , first pub l i shed in 1968 in England. 285 pages; 236 figures.

Chapter 1. Cam Mechanisms: Definition, types, manufacture, and accuracy.

Chapter 2. The Specification of Motion: Basic equations for popular cam motions and notes on dynamic considerations as related to machining accuracy.

Chapter 3. Cam Mechanism Geometry and The Calculation of Cam Profiles: Significance and analysis of pressure angle, profile curvature, and conditions of undercut; cutter coordinates for various configurations of swinging, radial, and conjugate cam systems.

Chapter 4. Direct Design of Cam Profiles: Kinematics of circular arc, straight flank, and eccentric disc c a m s .

Chapter 5. Forces in Cam Mechanisms: Analysis of component forces and driving torque requirement fcr specific configurations; inclusion of frictional components, design of restraining springs, and elements of system dynamics.

Chapter 6. Mechanism Design Practice: Practical design philosophy and procedures; frame details, bearing mountings, lubrication, and vibration considerations.

Chapter 7. Contour Cams and Band Mechanisms: Theory o f centrodes as related to rolling cam geometry; elliptic and hyperbolic contour cams with equivalent linkages; band mechanisms as function generators.

Chapter 8. Linkage Design: Forms and varieties of the four-bar linkage, Gruebler's criterion, number synthesis, Grashof's criterion, straight line and spatial linkages, graphical design of linkages.

Chapter 9. Projects for Study and Research: Suggested problems and studies designed to challenge the student and further the state of the art.

Appendix A. Special Generating Functions: Manipulation of motion functions to vary characteristics such as curvature and pressure angle.

Appendix B. Chebyshev's Polynomials: Function generators and the precision point approach.

Appendix C. What is Kinematics?: Author's definition of kinematic science and the development of vector loop approach to mechanism analysis.

Bibliography. One hundred and two references dealing with cam design, kinematics, and dynamics of mechanisms.

Classified Bibliography. Listing of selected authors under twelve specific mechanism areas.

IN HIS preface, the au thor defines the book as a pract ical work " for pract is ing engineers and for f inal-year or pos tg radua te s tudents do ing individual projects or research" . I t appears , however, that he is wri t ing for designers who have had little or no con tac t with

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kinematics or machine design as they are presently taught in undergraduate schools. While not a definitive work in mechanism design, the book does have value in pointing out problems that may arise in the design and analysis of machines. It is written in a clear and pleasant style, nicely sequenced, and with an abundance of descriptive figures.

In general, the book is a combination of detailed formulas for various cam geometry and mechanism forces and of general statements regarding factors that should be con- sidered in mechanism design. There is a chapter and two appendices which deal with linkages. These are of a general descriptive nature and only include a few kinematic design procedures. There is also a chapter of problems of various di,qiculty which corres- pond to the other sections of the book. The author does supply a fairly complete bibliog- raphy in the areas of cam design and kinematic linkage synthesis. His references and coverage in the areas of stress analysis and machine design are inadequate for the subject (mechanism design) of the book.

Its value as a first book in mechae.ism design is limited by the many expressions of attthor opinion as absolute fact. if these statements are not taken literally, the book could serve as a good survey of mechanism (especially cam) design practice.

Although the sevcral chapters on cam design include generalized formulas tbr cam displacement as a function of the popular follower motions, they are not in a form most easily applicable to data processing. Missing are the preferred rectangular coordinates for machining disc and barrel cams with swinging followers. Neither is there a study of the kinematics of roll followers about their own center of rotation or the discontinuity effects of backlash as required in dynamics analysis. Finally, the author states incorrectly that there are no rules for safe design of cam surfaces t¥om the standpoint of materials failure. Certainly there is nothing more impractical than a cam engineered to sophisticated kinematic standards but incapable of withstanding the imposed loads! Tests initiated in t932 by Buckingham at MIT are regularly producing surface endurance data for cams as summarized by Morrison in the August I, 1968, issue of Machine Design magazine.

The single chapter on linkage design starts with a fairly thorough and interesting description of the four-bar linkage and its possible forms. A brief discussion of Gruebler's criterion for the degrees of freedom of a linkage is included in the introductory section. This is followed by a brief section of kinematic synthesis procedures for problems of position guiding and function generating. The procedures are both graphical and analytical. After brief discussions of velocity and acceleration polygons for four-bar and slider-crank linkages, the chapter concludes with an input-torque analysis of a four-bar linkage.

It is surprising that a book on mechanism design which claims to be practical does not include design procedures for the drag-link or rocker-crank forms of the four-bar linkage. Also, the chapter does not consider the transmission angle--a measure of static force transmission comparable to the pressure angle of cam mechanisms. Design procedures for these practical forms of the tour-bar linkage and considerations of transmission angles appear in the kinematic texts which appear in the Bibliography.

Appendix C (What is Kinematics?) is an interesting approach to the definition of the science of kinematics and the development of the vector loop approach for the mathe- matical analysis of mechanisms. This Appendix affords the author a splendid opportunity to contradict himself. Here, he enthusiastically endorses the loop equation method of kinematic analysis of mechanisms because of its generality. Yet, his introductory remarks on mechanism design practice dogmatically reject complicated general analyses in favor of the simplest possible procedure for the specific device at hand.

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In conclusion, the author has selected material covering a broad spectrum of two complex areas but at the expense of occasional superficial treatment in both. This seems inevitable in a book of this size but the thinning out of nonessentials would afford valuable space for broader coverage of critical areas. For example, there are numerous books available which include the usual nostalgic grouping of mechanisms and provide the analysis of such limited and nearly obsolete designs as the circular arc cam. Needed is more up-to-date treatment of advanced cam production methods, materials analysis, working equations for the dynamic analysis of systems (including discontinuity effects), and compact presentation of design equations directly amenable to both hand and computer processing. Similar in-depth treatment of linkages and their relation to can: systems may best be delegated to a second volume.

RALPH MORRISON United Shoe Machinery Corp.,

Development Laboratories