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Page 1: Automatons

automatons

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WHAT IS A ROBOTThe Three Laws Of Robotics

(ISAAC ASIMOV)

A robot may not injure a human being, or, through inaction, allow a human being to come to harm.

A robot must obey the orders given it by human beings except where such orders would conflict with the First Law. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

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An autonomous robot is simply a self-contained robot that receives no assistance from outside, not even power.

WHAT IS AN AUTONOMOUS ROBOT

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THE BUILDING BLOCKS OF A ROBOT

Mechanical Blocks

Electronics

Computer Code Or Firmware

Intelligence

Shall we start …

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CHASSIS DESIGN

ACTUATORS

MOTORS-DC AND STEPPERS

WHEELS

CASTORS

MATERIALS FOR CHASSIS DESIGN AND TOOLS

WEIGHT AND POWER CONSIDERATIONS

BUILDING SMALL ROBOTS

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CHASSIS DESIGN

TRICYCLE

FOUR WHEELED DRIVE

TRACKED PLATFORMS

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TRICYCLE

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FOUR WHEELED DRIVE

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TRACKED PLATFORMS

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ACTUATORS

An actuator is a transducer that will convert one form of energy to mechanical movement.

For example a motor, hydraulic cylinders, solenoids etc

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MOTORS

A motor converts electrical energy to rotational movement.

TYPES OF MOTORS USEFUL FOR A ROBOT

DC MOTORS

STEPPER MOTORS

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Consists of two wires externally.

Turn clockwise or anticlockwise when either wire is at a higher potential than the other.

Normally have to be geared to provide working torque.

Robots that work autonomously should restrict speeds over 100 rpm for driving motors.

More In The Electronics' Part Of Dc Motors…

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These are motors that rotate in steps up on anexternal command.

Excellent when accurate positioning is required.

Have very minimal torque and hence design of the robot becomes critical

But are a good alternative to DC motors

They can consume larger currents as compared to DC motors of comparable sizes.

More In The Electronics' Part Of Steppers…..

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The next most important part of the robot is its wheels.

Wheels determine the pulling force of the robot, its speed, and actually its height.

A back of the hand formula is that the larger the wheel the lower the available force and higher the speed.

Select the lowest possible wheel diameter for the task at hand

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The simple calculation comes from the torque formula

F=r x T

So a larger wheel calculates to a high speed but a low pulling force

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WHEEL MATERIALS

Aluminium

Advantages

Looks very professional and robot looks neat. Highly load bearing and stiff Does not get corroded easily and will not sag or swell like wood.

Disadvantages

A little bit expensive but wheels last long.Slightly difficult to work with and hence have to be machined(actually bad when things fall off on last day)Slightly heavy and have to be spoked to reduce weight.

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NYLON

Advantages

Gives a clean lookLoad bearing and stiffDoes not get corroded easily and will not sag or swell like wood.Affordable and light weight.Has to be machined

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WOOD

Absolute no no!!

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CASTORS

A castor is a free wheel that can rotate in anydirection in one plane

A castor is a wheel that normally attached to trolleys, cabinets etc.

Such a wheel provides a third point of balance in tricycle type chassis and turns in any direction thus allowing smooth turns

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MATERIALS FOR CHASSIS DESIGN

ALUMINIUM

Available in various cross sections.

Can be easily visualised in the requisite shape.

But can be time consuming and demanding to cut, drill and bend.

Chassis is very lightweight and durable.

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ACRYLIC

Available in sheets of various thickness and sizes.

Can be cut, drilled very easily.

Cheap material for good design.

Brittle and not very strong.

Leaves irritating shavings after work.

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TOOLS

Hacksaw for both wood and metal.

Small bench vice.

Hand drill with standard bit sizes.

Other tools like hammer, pliers ,spanners etc

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BUILDING SMALL ROBOTS

All devices are miniaturised

Motors are available in small sizes

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SOME ADVICEMechanic assemblies are a one time investment

Build and machine good wheels and a stiff chassis

The best design is a two motor configuration with two castors as front wheels

Choose the smallest diameter possible.

The alignment should be very accurate and the robot should not be correcting itself every time because of misalignment.

Motors have to be dead straight.

Always this is achieved by a professional turner.

Weight of the robot should be as low as possible.

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SIGNAL REPRESENTATION,BOOLEAN LOGIC

THE PRINTER PORTDC and stepper motor introductionInterfacing to motors and sensors

MOTOR INTERFACING METHODSDC motorsStepper Motors

SENSORS AND CONFIGURATIONS

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Programmable Devices

Using Embedded Devices-Processors And Controllers

Introduction To Devices And Design

The Common Controller Families-8051, PIC And AVR

The ATMEGA8535-Controller For Robotic Applications

Features Of This Device And Peripherals

Interfacing To Motors And Sensors

Battery Technology And Regulators

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SIGNAL REPRESENTATIONSIGNAL REPRESENTATION AND BOOLEAN LOGICAND BOOLEAN LOGIC

Boolean logic is a branch of study that deals with quantitiesBoolean logic is a branch of study that deals with quantities represented by either yes(1) or no(0).represented by either yes(1) or no(0).

All decimal numbers can be broken down to digital numbers by using All decimal numbers can be broken down to digital numbers by using base 2 computation. base 2 computation.

In terms of voltages we assign 5V as logic 1 and 0V as logic 0 in In terms of voltages we assign 5V as logic 1 and 0V as logic 0 in digital electronics.digital electronics.

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THE PRINTER PORTTHE PRINTER PORT

The printer port is a 25 pin female connector found on most The printer port is a 25 pin female connector found on most modern computers.modern computers.

It is possible to command the printer port to set (1)or reset (0)It is possible to command the printer port to set (1)or reset (0)certain pins by writing a program on the computer. Such pins arecertain pins by writing a program on the computer. Such pins arecalled output pinscalled output pins

It is also possible to read the value of certain pins on the port and It is also possible to read the value of certain pins on the port and these can also be read by program. Such pins are called input pinsthese can also be read by program. Such pins are called input pins

So if we configure the motors to be connected (via a motor driver) toSo if we configure the motors to be connected (via a motor driver) tothe output pins and sensors to input pins, and use a certain logic tothe output pins and sensors to input pins, and use a certain logic tocontrol the motors depending on the sensor values, it is possible to control the motors depending on the sensor values, it is possible to control a robot whose parts are those sensors and motors.control a robot whose parts are those sensors and motors.

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THE PRINTER PORT PINSTHE PRINTER PORT PINS

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OUTPUTTING VALUES FROM THE PORTOUTPUTTING VALUES FROM THE PORT

The data port is used as the output port.The data port is used as the output port.

The address of the data port is 0x378(base) on most computers.The address of the data port is 0x378(base) on most computers.

In C if a command likeIn C if a command like

Outportb(0x378,4); // base=0x378Outportb(0x378,4); // base=0x378

Is executed then the value of data port pins will beIs executed then the value of data port pins will be

(0 0 0 0 0 1 0 0) // binary for 4(0 0 0 0 0 1 0 0) // binary for 4

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INPUTTING VALUES FROM THE PORTINPUTTING VALUES FROM THE PORT

There are two input ports on the printer portThere are two input ports on the printer portstatus port (base+1) and control port (base+2)status port (base+1) and control port (base+2)

Both have less than 8 pins as inputs and have to be Both have less than 8 pins as inputs and have to be used in conjunction for more inputs (upto 8)used in conjunction for more inputs (upto 8)

A statement like A statement like

int c;int c;c=inportb(0x379); // 0x379=base+1c=inportb(0x379); // 0x379=base+1

Will read the status port and store the read value in Will read the status port and store the read value in variable cvariable c

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DRIVING MOTORSDRIVING MOTORS The H-bridgeThe H-bridge

The H-bridge is a transistor based circuit that can input digital The H-bridge is a transistor based circuit that can input digital logic value and switch a connected motor clockwise or anticlockwise.logic value and switch a connected motor clockwise or anticlockwise.

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If switches A and D are on then current flow from the supply ,If switches A and D are on then current flow from the supply ,Switch A ,coil, switch D and ground.Switch A ,coil, switch D and ground.

If switches B and C are on then current flow from the supply ,If switches B and C are on then current flow from the supply ,Switch B ,coil, switch C and ground.Switch B ,coil, switch C and ground.

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THE L293 AND L298THE L293 AND L298

Both these integrated circuits are two H-bridges in a single package.Both these integrated circuits are two H-bridges in a single package.

They have 4 signal inputs that select witch transistor is on and 4 They have 4 signal inputs that select witch transistor is on and 4 output pins to which we connect motorsoutput pins to which we connect motors

Other pins include digital power, motor power, GND pins, inhibit Other pins include digital power, motor power, GND pins, inhibit pins and current limit pins.pins and current limit pins.

L293 is available in DIP package so has a rating of 1 AMP for bothL293 is available in DIP package so has a rating of 1 AMP for both bridges collectively.bridges collectively.

The L298 is a beefy version and can have a total rating of 2 AMPS withThe L298 is a beefy version and can have a total rating of 2 AMPS with a heat sink to be connected externally.a heat sink to be connected externally.

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L298L298

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STEPPER MOTORSSTEPPER MOTORS

TYPES OF STEPPER MOTORSTYPES OF STEPPER MOTORS Unipolar Motors(5 Wire Or 6 Wire)Unipolar Motors(5 Wire Or 6 Wire)

Bipolar Motors(4 Wire)Bipolar Motors(4 Wire)

All the above motors just about have the same internal windings All the above motors just about have the same internal windings but the difference come in the way they are drivenbut the difference come in the way they are driven

Unipolar motors can be driven by either discrete transistors or H Unipolar motors can be driven by either discrete transistors or H bridgesbridges

Bipolar motors are exclusively driven by H-bridgesBipolar motors are exclusively driven by H-bridges

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A stepper motor has four phase windings named A stepper motor has four phase windings named A B C D A B C D

When a phase is excited it means that thatWhen a phase is excited it means that thatphase has current flowing through itphase has current flowing through it

A particular phase sequence imparts rotationA particular phase sequence imparts rotation to the motorto the motor

The two excitation sequences areThe two excitation sequences are

HALF WAVE AND FULL WAVEHALF WAVE AND FULL WAVE

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HALF WAVE EXCITATIONHALF WAVE EXCITATION

The phase sequence for a particular direction of rotation isThe phase sequence for a particular direction of rotation isA-B-C-D-A-B-C-D-A-B …………A-B-C-D-A-B-C-D-A-B …………

To reverse the direction of rotation the sequence isTo reverse the direction of rotation the sequence isD-C-B-A-D-C-B-A ……..D-C-B-A-D-C-B-A ……..

FULL WAVE EXCITATIONFULL WAVE EXCITATION

The phase sequence for a particular direction of rotation isThe phase sequence for a particular direction of rotation isA- AB- B- BC- C- CD- D- DA- ……A- AB- B- BC- C- CD- D- DA- ……

To reverse the direction of rotation the sequence isTo reverse the direction of rotation the sequence isD- CD- C- BC- B- AB- A- ……D- CD- C- BC- B- AB- A- ……

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The ULN2803

This is an IC that contains 8 Darlington's with diode protection

This is used to control only an unipolar stepper motor

It is rated for 500mA and 36 V.

The cheapest solution to drive a stepper motor.

Every phase has to be individually set or reset.

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UCN 5804

This IC has in built logic to drive an unipolar stepper motor.

The only inputs that are required are clock, direction and whether the excitation is full or half wave.

Expensive.

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SPEED CONTROL OF MOTORS

DC MOTORS

Speeds of dc motors can be controlled by usingPulse width modulation or PWM

STEPPER MOTORS

Speed control can be done by changing the time Interval between two successive steps.

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SENSOR INTERFACING

The types of sensors are Active and Passive

Depending on the type the configuration of the sensor changes

For passive sensors the most common configuration is of a potential divider.

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LIGHT SENSORS

INFRARED SENSORS

These are two pin devices available in pairs-transmitter and receiver the transmitter is forward biased and the receiver is reversed biased.

When the receiver is irradiated with infrared light its resistance decreases.

PHOTOTRANSISTORS

These are three pin devices of which only two pins are used .

The configuration is same but this sensor is “blind” to infrared light

It has sensitivity to visible light

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ROBOT CONTROL USING PRINTER PORT

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LOOKING BACK

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MICROPROCESSORS ANDMICROCONTROLLERS

A microprocessor is a device that does sequencing of instruction that is written to its associated memory.

A microcontroller is same as a microprocessor but has its memory and other peripherals associated with it in a single IC package.

We will concentrate on microcontrollers but will dwell a little bit into microprocessors.Example 8085

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COMMON MICROCONTROLLER FAMILIES

8051

First microcontroller to be launched.

Very used and hence lots of programming resources.

8051 derivatives are also available with multiple Features.

Not a good choice for robotics applications.

Messy programming interface.

Still in use today for embedded applications.

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PIC-PERIPHERAL INTERFACE CONTROLLER

Good microcontroller family

Programming resources also available

Programmer mode is ICSP (In Circuit Serial Programmer)One programmer fits all devices

Available in variety of cost and features

Suited for small robotic applications.

Never used it !!!

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FEATURES OF ATMEGA85358 bit microcontroller with RISC architecture

On board 10 bit 8 channel ADC with highest sampling upto15 kHz

Onboard UART with independent receive and transmit registers

4 ports with high drive capability

8kb of on chip flash memory with ISP programmability

One programmer fits all devices

512 byte of SRAM and 512 bytes of EEPROM

3 timers with PWM function

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PROGRAMMER SCHEMATIC FOR AVR

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BATTERY TECHNOLOGY

OPTIONS FOR BATTERIES

SEALED LEAD ACID OR SLA BATTERIES

Ni-Cd BATTERIES

Ni-MH BATTERIES

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CELL CHARACTERSTICS

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VOLTAGEREGULATORS

These are three pin devices whose output voltage is approximately a constant over a large range of input conditions.

The 78XX series of voltage regulators is popular. The XX stands for the output voltage that a certain device will deliver. For e.g.

A 7805 voltage regulator will deliver output voltage at 5 volts.

These devices at least need input voltage about 2 volts higher than the output.

A 7805 regulator is required to provide constant voltage for logic circuitry.