basic robotics and sensors

8/13/2019 basic robotics and sensors

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Autonomous Robotics

PATH-FINDER

Robotics Club


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Difference b/w Machine and Robots

Reach

it


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Basics of mobile robot

Sensory devices for direction and feedback

Sensor data processing unit Actuators

Locomotion system

Control system for making decisions Power supply


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Some Most Common Sensors

Touch Sensor and IR Sensor


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Touch Sensors

One of the most simple ones---just a switch

force voltagemeasurement

electrical flow


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IR Sensor

This Consists of IR LED, IR sensor and a

variable resistance (preset).The LED continuously emits and when any

obstacle comes in front, the intensity is

increased at the sensors, hence changing

their state from OFF to ON.The range of these LEDs can be changed using

the preset (changing threshold).


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Light Sensor Photo Diode

This consists of a

photodiode which

allows current through

it, exponentially

proportional to light

absorbed by it, exactly

like a valve. It may or

may not require an

LED.

voltagemeasurement

light energy

electrical flow

voltagemeasurement

light energy

low light

bright light


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Light Sensors LDR

LDRs are light dependent resistances

Two circuits are possible as shown and theformula for them is

Rvariable

Rvariable


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Actuators

Wordweb:A mechanism that puts something

into automatic action. They convert electrical energy into

mechanical energy.

Motors provide rotational motion

Electromagnet provides linear motion


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Types of Motors

DC motors :Extensively used, all purposeones, driven by dc power supply

AC motor : not used in robotics, driven by acpower

Stepper motor: extensively used in robotics

where controlled rotation is required Servo motor: geared dc motor with inbuilt

feedback and error compensation


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DC Motor

Operates with dcvoltage

Can run in bothdirections

Speed control


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Working of a DC Motor

1. Direction of motion is controlled by polarity of voltageor direction of current

2. Speed is controlled by changing the average power

(energy) fed to the DC motor


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DC motor continued

DC motors are high speed and low torque

devices Gears are used to decrease the speed and

increase the torque

They give a smooth shaft movement

Easy to operate


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DC motor drivers

Drivers are current amplifier circuits

A low current control signal is convertedinto a proportionally higher current signal

that can drive a motor

But How????

Power Transistors---Those which

can handle current of the order of Amps


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Switching circuit


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H-bridge working


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Electronic direction control


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H-Bridge working


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Actual Circuit

When both the points A & B are "HIGH" Q1

and Q2 are in saturation. Hence the bases of Q3

to Q6 are grounded. Hence Q3,Q5 are OFF and

Q4,Q6 are ON . The voltages at both the motor

terminals is same, so the motor is OFF.

Similarly when both A and B are "LOW" the

motor is OFF. When A is HIGH and B is LOW,

Q1 saturates ,Q2 is OFF. The bases of Q3 and

Q4 are grounded and that of Q4 and Q5 are

HIGH.

Therefore Q4 and Q5 conduct making the right

terminal of the motor more positive than the left

and the motor is ON. When A is LOW and B is

HIGH ,the left terminal of the motor is more

positive than the right and the motor rotates in the

reverse direction. You can use only theSL/SK100s ,but BC148 used have a very low

hFE ~70 and they would enter the active region

for 3V(2.9V was what I got from the computer

for a HIGH) . You can ditch the BC148 if you

have a SL/SK100 with a decent value of hFE

( like 150).The diodes protect the transistors from

surge produced due to the sudden reversal of the

motor. The approx. cost of the circuit without the

motor is around Rs.40.


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DC motor Speed control circuit

Input: Operating voltage and control signal

Output: Part of operating voltage according

to control signal:


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DC Motor speed control continued.

Voltage across the terminal of Motor can be

changed by passing current through avariable resistor. But it is extremely energy

inefficient

A reduced average voltage is supplied to the

motor by a technique called PWM


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PWM

Pulse width modulation

PWM is a technique to generate waveformof different duty cycles depending upon an

input control voltage

After feeding voltage waveform and

changing its duty cycle ,speed can becontrolled.


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Duty cycle


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Duty cycle continue..

Time period (T): duration after which thevoltage waveform repeats itself

Duty cycle: % time of T when the voltage isequal to operating voltage

Average voltage:=

Duty cycle x operating voltage-------------------------------------

100


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PWM generation

Timer IC 555 is used for generation ofwaveform

Pin outs


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Circuit for PWM generation

Download Datasheet for NE555
http://www.downloadcatalog.com/http://www.downloadcatalog.com/


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Both speed and direction control


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L293D Quad Half H-Bridge


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Pin outs of L293D


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Stepper Motor

Widely use in Robotics ---why??

Because it is more precise than DC motorMeasured rotation and can be held at a

particular position

Alignation is much better in a differentialdrive


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Stepper motor continue


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Types of Stepper

Mainly of two types

Unipolarmotor: the current only flows in onedirection in the windings of the coils. i.e. the stator

poles can only be polarized one way.


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Continued.

Bipolar motor: the current flows in both

direction in the windings of the coils. i.e. the

stator poles can be polarized both way.


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Comparison

Unipolar

Current flow in one direction

Simple drive circuit

Less torque

Smooth drive

Bipolar

Current flow in both direction

Complicated drive Circuit

High Torque

Not Smooth


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Unipolar Stepper Motor

This kind of motor has four coils .

When energized in the correct sequence, it causes

the permanent magnet attached to the shaft to

rotate.

There are 4 basic step sequences. After step 4, the

sequence is repeated from step 1 again.

Reversing the order of the steps in a sequence will

reverse the direction of rotation.


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Single coil excitation

0010

0100

1000

0001


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a. Single-Coil Excitation - Each

successive coil is energized in turn.


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Double coil Excitation

0011 0110 1100 1001

Note:

The excitation of Coil 4 is always the inverse of the excitation of Coil 2.

The excitation of Coil 1 is always the inverse of the excitation of Coil 3.

So, with the right circuit, you can generate this sequence with only two

data lines.
http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.htmlhttp://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html


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b. Two-Coil Excitation - Each successive pair of

adjacent coils is energized in turn.


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Interleaving the two sequences will

cause the motor to half-step


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Single and Double coil Excitation1000 1100 0100 0110 0010 0011 0001 1001

0100 0011

0010

0110

01001100

1000

1001


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Comparison

Single coil

Low torque

Consume less energy

Settling time is more

Double coil

High torque

Consume double

energy Settling time is less


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Circuit Diagram


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The Coil Diagram


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Connections

DataPort1

Data

Port2

Motor 1

Motor 2

Note connect a 15v zener diode to pin 10 of IC as shown to prevent damageto the IC due to "back emf" when loads such as motors switch on and off


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25-way Female D-Type Connector


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PC parallel Port

The PC's Parallel Printer Port has a total of

12 digital outputs and 5 digital inputs accessed via 3

consecutive 8-bit ports in the processor's I/O space. 8 output pins accessed via the DATA Port

5 input pins (one inverted) accessed via the STATUS

Port

4 output pins (three inverted) accessed via theCONTROL Port

The remaining 8 pins are grounded

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basic robotics and sensors