ROBOTICS INTRODUCTION

 DEFINITION

The word ‘robot’ was introduced by Karel Cˇ apek a Czechoslovakian play writer in 1921.

The robot was derived from the Czech word ‘robota’ which suggests forced worker. Early writings

and plays during the 1920s and 1930s pictured the robot as a ferocious humanoid machine

which was intended for killing the citizenry.

Sir Isaac Asimov through his prodigious imagination contributed a number

of stories about robots starting from 1939. He coined the word ‘robotics’ which means the

science of robots. Later, Sir Isaac Asimov and Dr George Devol started a robotics industry

named as Unimation Inc. They started developing a fully hydraulic powered animate

robot. In later years, Ford Motors used ANIMATE successfully for die casting.

THE LAW OF ROBOTICS

The extended set of laws is as follows:-

The Meta-Law

A robot might not act unless its actions are subject to the laws of robotics.

Law Zero

A robot might not injure humanity, or through inaction, allow a people to return to harm

(humanity is the family of all citizenry and other biologically living things).

Law One

A robot might not injure a person's being, or through inaction, allow a person's being to return to harm unless this is able to violate a better order (an earlier stated) law.

Law Two

A robot must obey orders given by a person, except where such orders would conflict

with a better order law.

A robot must obey orders given by subordinate robots, except where such orders would

conflict with a better order law.

Law Three

A robot must protect the existence of a subordinate robot as long as such protection does

not conflict with a higher-order law.

A robot must protect its own existence as long as such protection does not conflict with

a higher-order law.

Law Four

A robot must perform the duties for which it has been programmed, except where that

would conflict with a higher-order law.

 

PRECISION OF MOVEMENT

Robot’s capability to succeed to some extent within its work volume depends on the precision of the robot. The precision of a robot may be a function of three features:

(i) Spatial resolution

(ii) Accuracy

(iii) Repeatability.

1.Spatial Resolution

 The spatial resolution of a robot is the smallest increment of movement during which the robot divides its entire work volume. the littlest increment in movement depends on two

factors – the robot’s mechanical inaccuracies and therefore the system control resolution.

Mechanical inaccuracies mainly come from robot joints. The joints generally have gears

and chains to manoeuvre the links

  The gear and chain drives have their non-linearities like back clash and hysteresis which create errors within the movement of robot link. within the case hydraulic and pneumatic drives at the joints, additional inaccuracies are created thanks to fluid

leakage and compressibility. These inaccuracies are added and magnified if the robot has

several joints, thus making the measurement of spatial resolution uncertain.

  

2.Accuracy

Accuracy refers to a robot’s ability to position its wrist end at the desired target point within

its work volume. The accuracy is related to spatial resolution because the accuracy depends

on how closely the neighbouring points are defined within the work volume and on how

accurately the mechanical structure is produced.

3.Repeatability

The same configurations of repeatability and accuracy in the dart game will also happen to a

robot. Assume a robot holds a pin at its gripper and is commanded to go to the target location

on a board, kept horizontal, again and again, and prick. By studying the test (pricked)

points, we can estimate the ability of the robot of repeatability and accuracy. In Figure 2.11, T is the location to which the robot is commanded to go.

DEGREES OF FREEDOM

We always work in a Cartesian coordinate system. In robotics, this is also known as the world

coordinate system or frame, since it is universally used in locating a point in the robot workspace. Even though other coordinate frames such as polar and spherical are also used in

robotics, we always prefer a robot to work in the Cartesian coordinate frame.

END EFFECTORS

 The end effector is an attachment to the wrist of a robot that permits to perform specialized

tasks. the perfect sort of a general-purpose end effector is to try to all the roles that human palm and fingers do.

  Human fingers have several joints and every joint has two or three DoF that can grasp, hold and manipulate the thing regardless of its shape and size. Robot manufacturers

and researchers around the world are working for achieving a cheap.

  The end effector has to grasp an object irrespective of its shape, hold it without the

objects coming out of the grasp, lift and shift the object to a new location and place it in a

specified orientation. The end effector also needs to do some processing functions such as

welding and screwing. There are wide varieties of end effectors required to perform different

industrial work functions.

GRIPPERS

 Grippers are wont to grip or grasp the objects. The objects (or parts) are generally the

workpieces that are to be manipulated by the robot. This aspect of part handling includes

machine loading and unloading, palletizing and picking parts from a conveyor. Figure 2.16

illustrates a number of the widely used grippers in industries.

Interchangeable finger pair is that the one which may be selected from several pairs and

attached to the wrist to suit the specified part size. Constricted fingers are suitable for handling

special contoured parts like cylinders and spheres. Standard angular and parallel

grippers are designed to select up smaller or larger sized parts of rectangular shapes.

Inflatable grippers are wont to handle cup-shaped parts. The inflatable cylindrical diaphragm

is inserted into the cup and inflated in order that the within the surface of the cup is held

firmly by the diaphragm.

      SENSORS

  INTERNAL AND EXTERNAL SENSORS

Following are two principle kinds of robot sensors:

(i) Internal sensors: These are fitted internally to the robot structure. Sensors for position

and velocity of a servo motor are the internal sensors. They are inherent to a robot’s basic

control system. Their main function is to assist in creating feedback for achieving an

accurate servo control system for robot joint manipulation. Potentiometers, resolvers

and tacho-generators are internal sensors for a robot to measure position and velocity.

(ii) External sensors: Sensors other than internal sensors are termed as external sensors.

Sensors to detect the presence of an object in a conveyor ( proximity sensors) to

indicate the distance between object and gripper ( range sensors) and to exert a suitable grip to objects ( force sensors) are some examples of external sensors. External sensors help a robot to interact with environmental changes.