Introduction of Kinematics of Machines

Introduction

The subject Kinematics of Machines also known as KOM is a very special course for the Mechanical Engineers. This course tells us about the distinctive features of the machines. This tells us how the machine works. In this course, we will study about the working of the machines. How they work? What would be the speed of output is some input speed is given. What would be the acceleration and so on.

So there are two parts, one is kinematics and the other part is machines. First we tell about the kinematics.

Kinematics:

Kinematics is the branch of mechanics which tells us about the motion without considering the cause of motion. In this portion, we study the displacement, speed and acceleration without bothering about the input force or torque.

Dynamics:

In this, we study about the effect of force and torque on an object. We study about the output velocity, acceleration, when the input torque or force is given.

Prerequisite for the course:

You should have the knowledge of following items before starting this course:

1. Vectors

2. Concepts of displacement, velocity and acceleration

3. Basic mechanics.

4. And some part of engineering graphics.

Machines:

The main part of this course is the study of machines. A machine is a tool which converts one form of energy to some useful work. For example an engine converts thermal energy into mechanical energy. So the engine would be a machine. A lathe machine converts electrical energy into some useful mechanical work, so it is a machine.

Although, we will discuss the machine in detail in later part of the tutorials, but the basic definition is “A machine is a combination of rigid or resistant bodies, formed and connected do that they move with definite relative motions and transmit force from the source of power to the resistance to be overcome. A machine has two functions: transmitting definite relative motion and transmitting force.  These functions require strength and rigidity to transmit the forces.”

MECHANISM AND MACHINES

Mechanism: A mechanism is a constrained kinematic chain. This means that the motion of any one link in the kinematic chain will give a definite and predictable motion relative to each of the others. Usually one of the links of the kinematic chain is fixed in a mechanism.

Fig.1.01 Slider crank and four bar mechanisms.

If, for a particular position of a link of the chain, the positions of each of the other links of the chain cannot be predicted, then it is called as unconstrained kinematic chain and it is not mechanism.

Fig.1.02 Unconstrained kinematic chain

Machine: A machine is a mechanism or collection of mechanisms, which transmit force from the source of power to the resistance to be overcome. Though all machines are mechanisms, all mechanisms are not machines. Many instruments are mechanisms but are not machines, because they do no useful work nor do they transform energy. Eg. Mechanical clock, drafter.

Fig.1.03 Drafter

Planar mechanisms: When all the links of a mechanism have plane motion, it is called as a planar mechanism. All the links in a planar mechanism move in planes parallel to the reference plane.

KINEMATICS LINKS

Link or element: It is the name given to any body which has motion relative to another. All materials have some elasticity. A rigid link is one, whose deformations are so small that they can be neglected in determining the motion parameters of the link.