The student is cautioned to always check the units in any equation written for a prob- lem solution, whether in school or in professional practice after graduation. If properly written, an equation should cancel all units across the equal sign. If it does not, then you can be absolutely sure it is incorrect. Unfortunately, a unit balance in an equation does not guarantee that it is correct, as many other errors are possible. Always double-check your results. You might save a life.
1.11 WHAT'S TO COME
In this text we will explore the topic of machine design in respect to the synthesis of mechanisms in order to accomplish desired motions or tasks, and also the analysis of these mechanisms in order to determine their rigid-body dynamic behavior. On the premise that we cannot analyze anything until it has been synthesized into existence, we will first explore the topic of synthesis of mechanisms. Then we will investigate the analysis of those and other mechanisms for their kinematic behavior. Finally, in Part II we will deal with the dynamic analysis of the forces and torques generated by these moving machines. These topics cover the essence of the early stages of a design project. Once the kinematics and kinetics of a design have been determined, most of the concep- tual design will have been accomplished. What then remains is detailed design-sizing the parts against failure. The topic of detailed design is discussed in other texts such as reference [8].
INTRODUCTION
Vorioble
Force Length Time Mass Weight Velocity
Acceleration Jerk
Angle Angle
Base Units in Boldface — Abbreviations in ( )
Symbol ips unit
£ pounds (lb)
/ inches (in)
/ seconds (sec)
lb—sec2 / in (bl)
W pounds (lb)
lps unit
pounds (lb) feet (ft) seconds (sec) lb—sec 2 / ( ) pounds (lb)
ft / sec
« / sec2 ft / sec!
degrees (deg) radians (rad)
m / sec! degrees (deg) radians (rad)
Angular veloci Angular acceleration Angular jerk
Torque
Mass moment of inertia Energy
Power Volume
Weight density Mass density
rad / sec
rad / sec! rad / sec 3 lb—ft lb—ft—sec 2 ft—lb
ft—lb / sec ft3
lb / It’ sI / It'
rad / sec rad / sec 2 rad / sec! N—m
N—in—sec! joules watts
REFERENCES
de Jonge, A. E. R. (1942). “What Is Wrong with ‘Kinematics’ and ‘Mechanisms’?”
Mechanical Engineering, 64(April), pp. 273-278. 连杆机构英文文献和中文翻译(13):http://www.youerw.com/fanyi/lunwen_79963.html