Introduction to Mechanism Design

with Computer Applications

Eric Constans, Karl B. Dyer

• Verlag: CRC Press
• Jahr: 2018
• ISBN:
  9781351727617
• Auflage: 1
• Thema: Technology & Engineering
• Thema: Civil Engineering

Introduction to Mechanism Design: with Computer Applications provides an updated approach to undergraduate Mechanism Design and Kinematics courses/modules for engineering students. The use of web-based simulations, solid modeling, and software such as MATLAB and Excel is employed to link the design process with the latest software tools for the design and analysis of mechanisms and machines. While a mechanical engineer might brainstorm with a pencil and sketch pad, the final result is developed and communicated through CAD and computational visualizations. This modern approach to mechanical design processes has not been fully integrated in most books, as it is in this new text.

1

Introduction to Kinematics

1.1 Introduction to Mechanical Design

The subject of this textbook is mechanical design and analysis. While most people have at least a vague idea of what the word “design” means, in this text we are mainly interested in two definitions [1]:

Design:

transitive verb 1. To make preliminary sketches of; sketch a pattern or outline for; plan. 2. To plan and carry out, esp. by artistic arrangement or in a skillful way. …

intransitive verb 8. the arrangement of parts, details, form, color, etc. so as to produce a complete and artistic unit

The goal of the text is to give the reader a set of computational tools to design and analyze mechanisms to achieve specific goals. A mechanism is a collection of links and joints designed in such a way as to create a desired motion output. One link of a mechanism is “grounded,” that is, fixed to some reference frame, and we are commonly interested in finding the motion of the remaining links. Some examples of mechanisms are windshield wiper blades, the crankshaft/connecting rod/piston assembly in a car engine, certain types of hinges, mechanical watches and clocks, etc. Another excellent example of a mechanism, or linkage, is the human body. Each segment of the body can be modeled as a link, and the segments are connected through pin joints (the elbow) or spherical joints (the shoulder). By modeling the body in this way, biomechanical engineers can deduce the forces and moments present at the joints by analyzing the motion of the body with motion capture techniques.

Scientists, mathematicians, and engineers have studied mechanisms since the 1700s. Until very recently, all mechanism analysis was performed graphically, that is, with drafting tools. These tools have been superseded in modern times by computational tools such as CAD software, which make it possible to analyze several trial designs very quickly to find a solution. Computers have also made “linkage design optimization” possible; that is, finding the dimensions of a linkage that traces out a desired path.

The majority of the book covers the kinematic analysis of mechanisms:

Kinematics: the study of motion without regard to forces.

The first section of the book provides an introduction to some fundamental concepts in kinematics, and the student will learn techniques for designing linkages with CAD software, such as SOLIDWORKS^®. Afterwards, we discuss methods for predicting the motion of linkages using computer programs written in MATLAB^®. This is actually a rather difficult task, and will take up most of the text. To begin this task, we will learn how to find the positions traced out by a given linkage. Once we are able to compute positions of linkages, it is a simple matter to compute velocities and accelerations. Accelerations must be calculated to analyze link forces, as well as to keep accelerations within limits that can be tolerated by human beings. Once the motion of a linkage has been determined, the next step is to perform kinetic (dynamic) analysis.

Kinetics: the study of forces on a system in motion.

Force analysis is necessary to keep forces (stresses) within acceptab...