Kinematic analysis and synthesis
Kinematic analysis and synthesis are used to study the motion or position of a set of rigid bodies in a system without reference to the forces causing that motion or the mass of the bodies (Fig. 10). It allows engineers to see how the mechanisms they design will function
in motion. This luxury enables the designer to avoid faulty designs and also to apply the design to a variety of scenarios without constructing a physical prototype. Synthesis of the
data extracted from kinematic analysis in numerous iterations of the process leads to optimization of the design. The increased number of trials that kinematic analysis allows the engineer to perform may have profound results in optimizing the behavior of the resulting mechanism before actual production.
Static analysis determines reaction forces at the joint positions of resting mechanisms when a constant load is applied. As long as zero velocity is assumed, static analysis can also be performed on mechanisms at different points of their range of motion. Static analysis allows the designer to determine the reaction forces on whole mechanical systems as well as interconnection forces transmitted to their individual joints. The data extracted from static analysis can be useful in determining compatibility with the various criteria set out in the problem definition. These criteria may include reliability, fatigue, and performance considerations to be analyzed through stress analysis methods.
Dynamic analysis combines motion with forces in a mechanical system to calculate positions, velocities, accelerations, and reaction forces on parts in the system. The analysis is performed stepwise within a given interval of time. Each degree of freedom is associated with a specific coordinate for which initial position and velocity must be supplied. Defining the system in various ways creates the computer model from which the design is analyzed. Generally, for data relating to individual parts, the user must supply geometry, forces, and
overall system coordinates either directly or through a manipulation of data within the software. The results of all of these types of analyses are typically available in many forms, depending on the needs of the designer. All of these analytical methods will be discussed in greater detail in Section 7 relating to CAD software.
Experimental analysis involves fabricating a prototype and subjecting it to various experimental methods. Although this usually takes place in the later stages of design, CAD systems enable the designer to make more effective use of experimental data, especially where analytical methods are thought to be unreliable for the given model. CAD also provides a useful platform for incorporating experimental results into the design process when experimental analysis is performed in earlier iterations of the process.Design review can be easily accomplished using CAD. The accuracy of the design can be checked using automated tolerancing and dimensioning routines to reduce the possibility of error. Layering is a technique that allows the designer to superimpose images upon one another. This can be quite useful during the evaluative stage of the design process by allowing the designer to visually check the dimensions of a final design against the dimensions of
stages of the design’s proposed manufacture, ensuring that sufficient material is present in preliminary stages for correct manufacture. Interference checking can also be performed using CAD. This procedure involves making sure that no two parts of a design occupy the same space at the same time.
COMPUTER-AIDED DESIGN
Emory W. Zimmers, Jr. and Technical Staff
Enterprise Systems Center
Lehigh University
Bethlehem, Pennsylvania
Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
Copyright 2006 by John Wiley & Sons, Inc.
