Robotics@Techweek’07

What is a Robot? Electro-mechanical device. Performs Various tasks. May be human controlled or automated. It finds it’s uses in all aspects of our life.

How a Robot Can Help ? An automatic industrial machine replacing the human in hazardous work environment. An automatic mobile sweeper machine at a modern home. An automatic toy car for a child to play with. A machine removing mines in a war field all by itself and many more…

Basic Parts of a Robot Mechanical system Power supply system Actuators Sensory devices for feedback Sensor Data processing unit Control system

Mechanical Systems

Mechanical System The most basic and important part of the robot. It comprises of chassis, motors, wheels and their placement. This system decides the locomotion of the robot.

Wheeled Locomotion Systems Differential drive Car type drive Skid steer drive Synchronous drive Pivot drive

Differential Drive This is the most commonly used form of locomotion system used in robots as it’s the simplest and easiest to implement. It has free moving wheel(s) in the front accompanied with a left and right wheel. The two wheels are driven by different motors.

Differential Drive Cont…

Differential Drive: An Analysis Simplicity and ease of use makes it the most preferred system by beginners Independent drives makes it difficult for straight line motion. The differences in motors and frictional profile of the two wheels cause them to move with slight turning effect The above drawback must be countered with appropriate feedback system. Suitable for human controlled remote robots

Car Type Drive It is characterized by a pair of driving wheels and a separate pair of steering wheels. The translation and rotation are interlinked, hence this system faces severe path planning problem.

Car Type Drive Cont…

Skid Steer Drive A close relative of the differential drive system. It is mostly used in tracked machines e.g. tanks. Also finds application in some four / six wheeled robots The left and right wheels are driven independently. Steering is accomplished by actuating each side at a different rate or in a different direction, causing the wheels or tracks to slip, or skid, on the ground.

Skid Steer Drive Cont…

Synchronous Drive As the name suggests, it uses synchronous rotation of its wheels to achieve motion & turns It is made up of a system of motors. One set of which drive the wheels and the other set turns the wheels in a synchronous fashion The two sets can be directly mechanically coupled as they always move in the same direction with same speed

Synchronous Drive Cont…

Pivot Drive The most unique type of Locomotion system It is composed of a four wheeled chassis and a platform that can be raised or lowered

Pivot Drive Cont… The wheels are driven by a motor for translation motion in a straight line For rotation one motor is needed to lower/raise the platform & another to rotate the chassis around the platform This system can guarantee perfect straight line motion as well as accurate in – place turns to a desired heading

Power Systems

Power Supply System Suitable power source is needed to run the robots. Robots are most suitably powered by batteries. The weight and energy capacity of the batteries may become the determinative factor of its performance.

Actuators

Actuators They convert the electrical energy into meaningful mechanical work Mechanical output can be rotational or linear (straight line) Motors provide rotational motion Electromagnets provide linear motion

Motors are of various kinds AC Motors : Not used much in robotics Stepper Motors : For controlled rotation DC Motors : Finds extensive general use Servo Motors : DC motor with in built feedback & error compensation

Stepper Motors Used for measured rotation. Can be held at a particular position of the shaft. Ideal for many autonomous robots requiring higher precision.

Stepper Motor Working 1000 0100 0010 0001 Stepping Sequences for Single Coil Excitation Only one coil is active at a given instant of time

Single Coil Excitation

Stepper Motor Working Cont… 1100 0110 0011 1001 Stepping Sequences for Double Coil Excitation Two coils active at any given instant of time

Double Coil Excitation

Problems with Stepper Motors Very low torque to weight ratio Torque decreases with increase in the stepping frequency For sufficiently high stepping speed the stepper motor may skip steps due to overshoot

DC Motors As the name suggests, a motor which uses a DC (Direct Current) power Can run in both directions Speed Controllable

DC Motor Characteristics DC Motors are high–speed, low-torque devices. Using gears, the high speed of the motor is traded off into torque

DC Motor Drivers These are current amplifying circuits. A low current control signal is converted into a proportionally higher current signal that can drive the motor

DC Motor Direction Control Power Transistor Switches VCC S1 S2 M 1 2 S3 S4 H – Bridge Circuit Diagram

H – Bridge Working S1 S2 S3 S4 Current Direction Effect 1 1 to 2 1 to 2 Motor spins forward 2 to 1 Motor spins backward - Braking Occurs

Electronic Direction Control H – Bridge Circuit Diagram

Control Systems

Open Loop Control System Desired Action Controller Controller Actuator Actuator There is no error correction. No way to check if the actuator was able to take the desired action Simple system to design, not very reliable Requires regular calibration of the system

Closed Loop Control System Desired Action Controller Actuator Feedback

Example : An Air conditioner Room Temp Cooling Device Desired Temp. Controller Temperature Sensor

Sensors

Sensors Analogous to human sensory organs Eyes, ears, nose, tongue, skin Sensors help the robot knowing its surroundings better Improves its actions and decision making ability Provides feedback control

Examples Light Dependent Resistor Thermistor IR Photo Sensor

Line Follower

Line Follower A line follower is a robot capable of tracking a line drawn on a surface Optical sensors capture the line position at the front end of the robot The robot is steered to keep it always over the line Click to view

Optical Reflectors

Sensor Interfacing

Project DCE AUV

Delhi College of Engineering

Description Tasks and Arena

CONSTITUTION Mechanical Design Power 50 Embedded Control Systems Electronics Programming Power Mechanical Design Power Embedded Control Systems 50

The Vehicle

Test and Performance

Thank You