Mechanisms and Machines: Basic Concepts

Chapter: 1

Mechanisms and Machines: Basic Concepts

Learning Objectives

While reading and after studying this chapter, you will be able to:

• Understand the basic concepts (such as links, kinematic pairs, kinematic chains, joints) relevant to the study of mechanisms and machines.

• Describe various types of constrained motions and different kinds of kinematic pairs.

• Derive the Kutzbach and the Grubler's criteria to determine the degree of freedom of a planar mechanism.

• Differentiate between mechanism and machine; machine and structure; lower pair and higher pair.

• Sketch and explain the various inversions of four-bar chain.

• Sketch and explain the various inversions of slider-crank chain and double slider-crank chain.

SYLLABUS

Mechanisms and Machines: Basic Concepts

Mechanisms - Kinematic link, pair, chain - Degrees of freedom  - Kutzbach and Grubler's criterion – Inversion of mechanisms – Inversions of four-bar chain, single slider-crank chain, and double slider - crank chain.

INTRODUCTION

• Since this book is all about mechanisms and machines, therefore it is essential to understand the meaning of those terms first.

• Mechanisms Machine:

• A mechanism is a device to transmit and modify motion. If the device also transmits forces, in addition to motion, then the device is called as machine.

• In other words, a machine is a device which transmits both motion and forces. A machine may consists of one or more mechanisms for transmitting both motion and forces.

• In fact, all machines are mechanisms, but all mechanisms are not machines.

• For example, the drafter (Fig.1.1) is a mechanism, not a machine. Because the after is used to transmit motion of links a definite manner. It does no useful work nor it transmits energy.

• Examples for machines: Internal combustion engines, shaper and planar in workshop, sewing machine, etc.

• Examples for mechanisms: Drafter, typewriter, mechanical clocks spring toys, common hand tools (such as scissors, screwdrivers, and wrenches), etc.

• The term machinery means an assembly that includes both machines and mechanisms.

• The study of mechanisms involves both their analysis as well as synthesis, as shown in Fig.1.2.

In this chapter, we shall discuss the definitions and basic concepts relevant to the study of mechanisms and machines.