robotic actuators and sensors by MAHENDRA BABU MEKALA OF pbrvits, kavali

8/3/2019 robotic actuators and sensors by MAHENDRA BABU MEKALA OF pbrvits, kavali

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Robot Actuators

Stepper motors

DC motors

AC motors

Physics review:

Electric fields and magnetic

fields are the same thing.

Nature is lazy.Things seek lowest energy states. iron core vs. magnet magnetic fields tend to line up

v+ - v+ -

N

S

N S


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Stepper Motor Basics

S

N

Stator: made out of coils ofwire called winding

Rotor: magnet rotates onbearings inside the stator

Direct control of rotor position (no sensing needed)

May oscillate around a desired orientation (resonance at low speeds)

Low resolution

printers

computer drives

SN

Electromagnet

stator

rotor

N S

Current switch in winding

==>Magnetic force

==>hold the rotor in a position


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Increased Resolution

Half stepping

S

S

N

N

angle

torque


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More teeth on rotor or stator

Half stepping

S

S

N

N


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More teeth on rotor or stator

Half stepping

S

S

N

N


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How to Control?

Step TableStep Red Blue Yellow White

0 + - + -

1 - + + -

2 - + - +

3 + - - +

4 + - + -

4 l e a d

m o t o r

R e d

B l u e

A +

A -

B + B -

Y e l l o w W h i t e

4 Lead Wire Configuration

Clockwise Facing Mounting End

Increase the frequency of the steps => continuous motion

Each step, like the second hand of a clock => tick, tick


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Motoring along...

direct control of position

precise positioning (The amount of

rotational movement per step depends

on the construction of the motor)

Easy to Control

under-damping leads to oscillation at low speeds

torque is lower at high speeds than the primary alternative


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DC motors -- exposed !


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DC motor basics

N

S

N S

stator

rotor

permanentmagnets

commutatorattached to

V

+

-

brush


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DC motor basics

N

S

N S

stator

rotor

permanentmagnets

N SS N

V

+

-

V

+

-


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DC motor basics

N

S

N S

stator

rotor

permanentmagnets

N SS N N SN S

V

+

-

V

+

-

V

+

-


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12

Robotics Sensors

Sensors collect all the information a robot needs to

operate and interact with its environment.

What are sensors?

What are Controllers?

Controllers interpret all the input from the sensors

and decide how to act in response.


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Robotics Sensors

What are sensors for?

The control of a manipulator or

industrial robot is based on the

correct interpretation of sensory

information. This information can

be obtained either internally tothe robot (for example, joint

positions and motor torque) or

externally using a wide range of

sensors.


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Robotics Sensors

Since sensors are any device thatprovide input of data to the robotcontroller a wide verity of sensors exist.Some basic types of sensors are shownincluding:

Light sensors which measure light

intensity. Heat Sensors which measure

temperature. Touch sensors which tell the robot when

it bumps into something. Ultra Sonic Rangers which tell the robot

how far away objects are.And gyroscopes which tell the robot

which direction is up.

Types of Sensors


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Robotics Sensors

The bumper skirt on this robot

is an example of a touch sensor.

When the robot runs into a wall

the bumper skirt hits a micro

switch which lets the robot

controller know that the robot is

up against a wall. Other types of

touch sensors are used

internally to let the robot knowwhen an arm is extended to far

and it should be retracted or

when the robots other physical

limits are reached.


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Light sensors are used todetect the presence andIntensity of light. Thesecan be used to make alight seeking robot andare often used to simulateinsect intelligence inrobots.

Robotics Sensors


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Heat sensors help robots

determine if they are in

danger of overheating.These sensors are often

used internally to make

sure that the robots

electronics do notbreakdown.

Robotics Sensors


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Ultra Sonic Rangersare used todetermine how far arobot is away from

an object. They areoften used by robotsthat need to navigatecomplicated terrain

and cannot riskbumping intoanything.

Robotics Sensors


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Gyroscopes are used inrobots that need tomaintain balance or are

not inherently stable.Gyroscopes are oftencoupled with powerfulrobot controllers that

have the processingpower necessarycalculate thousands ofphysical simulations per

second.

Robotics Sensors


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Position Sensors

Optical Encoders

Relative position

Absolute position

Other Sensors

Resolver Potentiometer


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Optical Encoders

Relative position- direction- resolution

grating

light emitter

light sensor

decode

circuitry


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Ideal

Optical Encoders

Relative position mask/diffuser

gratinglight emitter

light sensor

decode

circuitry

Real

A diffuser tends to

smooth these signals


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Optical Encoders



light sensor

decode

circuitry


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Optical Encoders



light sensor

decode

circuitry

A

B

A

B

A lags B


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Optical Encoders



light sensor

decode

circuitry

A

BA leads B

Phase lag between A and B is 90 degree


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Optical Encoders

Detecting absolute position

something simpler ?


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Optical Encoders

Detecting absolute position

wires ?


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Gray Code

0

1

2

3

4

5

6

7

8

9

# Binary

0

1

10

11

100

101

110

111

1000

1001

000

001

011

010

110

111

101

100

among others...


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Other Sensors

Resolver

= driving a

stepper motor

Potentiometer

= varying

resistance


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Robot Sensors

Why do Robots Need Sensors?

What can be Sensed?

What Sensors are Out There? What can They do?

How Much do They Cost? How Easy are They to Use?


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Why Do Robots Need Sensors?

Provides awareness of surroundings Whats ahead, around, out there?

Allows interaction with environment

Robot lawn mower can see cut grass Protection & Self-Preservation

Safety, Damage Prevention, Stairwell sensor

Gives the robot capability to goal-seek Find colorful objects, seek goals Makes robots interesting


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Sensors - What Can Be Sensed?

Light Presence, color, intensity, content (mod), direction Sound

Presence, frequency, intensity, content (mod), direction

Heat Temperature, wavelength, magnitude, direction Chemicals

Presence, concentration, identity, etc.

Object Proximity Presence/absence, distance, bearing, color, etc. Physical orientation/attitude/position

Magnitude, pitch, roll, yaw, coordinates, etc.


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Sensors - What Can Be Sensed?

Magnetic & Electric Fields Presence, magnitude, orientation, content (mod)

Resistance (electrical, indirectly via V/I)

Presence, magnitude, etc.

Capacitance (via excitation/oscillation) Presence, magnitude, etc.

Inductance (via excitation/oscillation) Presence, magnitude, etc.

Other Things?


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What Sensors Are Out There?

Feelers (Whiskers, Bumpers) Mechanical

Photoelectric (Visible) Active & Passive

Infrared (light) Active & Passive Ultrasonic (sound) Active & Passive

Sonic Active & Passive

Resistive/Capacitive/Inductive Active &Passive


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What Sensors Are Out There?

Visual Cameras & Arrays (Active & Passive)

Color Sensors (Active & Passive)

Magnetic (Active & Passive)

Orientation (Pitch & Roll)

GPS (location, altitude)

Compass (orientation, bearing)

Voltage Electric Field Sensors Current Magnetic Field Sensors

Chemical Smoke Detectors, Gas Sensors


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A Closer Look


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Sensors Feelers

Whiskers Piano wire suspended through conductive hoop Deflection causes contact with hoop Springy wire that touches studs when deflected

Reaches beyond robot a few inches Simple, cheap, binary output

Bumpers & Guards Impact/Collision sensor, senses pressure/contact Microswitches & wires or framework that moves Simple, cheap, binary output, easy to read


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Feelers - Whiskers


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Feelers - Bumpers & Guards

From Kevin Rosss Getting Started Article (SRS Website)


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Sensors IR

Active (emitting) Oscillator generates IR reflections off objects Filtered receiver looks for reflections Pulses may be encoded for better discrimination

Typically frequencies around 40KHz Doesnt work well with dark, flat colored objects

Passive (sensor only) Pyro-electric (heat sensor) Look for IR emissions from people & animals Used in security systems & motion detectors


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Infrared - Active

$30 from Lynxmotion

July 99 Encoder


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Active IR Sensor Specs

Sensor type = Reflective IR

IR detector = Panasonic PNA4602M

IR LED type = Narrow focus 10

I/O required = 3 digital lines: 2 outputs, 1 input

Range = Approximately 4 to 26"

Input voltage = 5vdc regulated @ 8mA

PC board size = 2.3" x .75"


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Linear Array IR Range Sensors

Sharp GP2Dxx (one of many) ~4 to 30cm Range

Fixed Range with Discrete Output

Analog or Digital Output

Easy to Use


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Laser Range Sensors

USB Interface

240 Field of View

0.36 Angular Resolution

10Hz Refresh Rate

20mm to 4m

$2695 (cool but pricey)

Also See: Oct 2001 Encoder

Kenneth Maxon


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Passive IR Pyro-Electric

$66 from Acroname

Dec 2000, Sept 2001 Encoder

The Model 442-3 IR-EYE is a Lithium Tantalate pyroelectric parallel opposeddual-element high-gain detector with complete integral analog signal processing.


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Sensors Ultrasonic

Active Emit pulses & listen for echos Times round trip sound travel (~1ft/mS) Reaches far fairly beyond robot (inches to 30-50)

Relatively simple, not cheap, analog output Directional; not everything reflects sound well

Passive (listens only) Sensor listens for ultrasonic sounds Electronics may translate frequency or modulation

Software may perform signal analysis (FFTs, etc.)


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Ultrasonic - Active

$27

$134$49

Visit http://www.acroname.com for more information about these & other products.

Search the web for polaroid ultrasonic sensor


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Sensors Ultrasonic (cont.)

Passive - Beacons & Sensors Beacons listen: RF command to broadcast

Send light & sound pulses Robot looks & listens for each beacon

Light pulse starts timer, sound pulse stops it Robot knows location of each beacon Compass on robot provides its orientation

Robot computes distance, measures bearing

Robot can then compute its location

(Speed of Light=1 ft/nS, Speed of

Sound=1ft/mS)


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Ultrasonic - Passive

Beacon1

Beacon2

Sound Pulse

Sound Pulse

Robot

Light PulseBEACON

RF Receiver

IR Emitter

Ultrasonic Emitter

Beacon3

Light Pulse

Sound Pulse

ROBOT

RF Transmitter

IR Receiver

Ultrasonic Receiver

Light Pulse


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Sensors Sonic (Acoustic) Active

Emit pulses & listen for echos Times round trip sound travel (~1ft/mS) Reaches far fairly beyond robot (30-50 ft) Relatively simple, not cheap, analog output

Directional, not everything reflects sound Noisy!!!!

Passive (sensor only)

Sensor listens to ambient sounds Filters or scans selected frequenciesADC measures conditioned signal amplitude CPU performs signal analysis on what it hears


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Sonic (Acoustic) - Passive

TI (Burr-Brown) UAF42 Universal Active Filter

http://focus.ti.com/lit/an/sbfa002/sbfa002.pdf


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Sensors Resistance

Passive (sensor only) Measures elec. resistance between objects

Measure sensor that varies resistance Use absolute or differential readings Other ideas?


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Sensors Capacitive

Passive

Really doesnt work (Needs excitation)

Active (emitting) Generate AC or DC voltageApply to external environment

Measure current to determine Resistance Short range applications


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Sensors - Capacitive


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Sensors - CapacitiveEmit an electric field below the sensor.

Nulled to a known void wall area.Detect capacitance difference due to underlyingmaterial density.


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Sensors Inductive

Passive Really doesnt work (Needs excitation)

Active (emitting) Current flows through inductor

Magnetic field mostly ignores non-metals

Inductance changes with metallic proximity Short range applications

S I d ti


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Sensors - Inductive Passive

Really doesnt work (Needsexcitation)

Active (emitting) Metals affect sensor Current flows through inductor

Magnetic field mostly ignores non-

metals Inductance changes with metallic

proximity

Short range applications (~cm or mm)


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Sensors Visual

Active (emitting) Camera with field of view illumination Looks for particular reflections

Filter removes non-significant light sources Linear array senses single axis of motion

Passive (camera only) Scans field of interest Looks for objects, artifacts, features of interest Processes digital data to simplified interpretation


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Sensors Visual

CMUCam

Linear Optical Array


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Sensors Color

Active (emitting) Selective field illumination (specific color(s)) Sensor filter removes extraneous light sources

Output can be analog (prop.) or digital (on/off)

Passive (sensors only)

Different sensors for different colors Color filter removes extraneous light sources Output can be analog (prop.) or digital (on/off)


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Sensors Color

http://robotroom.com/ColorSensor.html


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Sensors Magnetic

Active (emitting) Metal detectors

Follows metallic strips on or under the floor

Magnetometer Magnetic Resonance Imaging (MRI)

Passive (sensors only) Compass Magnetic field sensor (oscillating current)


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Sensors Magnetic

From HowStuffWorks.com & RadiologyInfo.org


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Sensors Orientation

Rate Gyros

Output proportional to angular rotation speed

Integrate to get position

Differentiate to get acceleration

DC Accelerometer

Output proportional to sine of vertical angle


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Sensors Motion

Rate Gyro Silicon Sensing SystemsServo Accel Sensorland.com


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Sensors Position/Location

Wheel Encoders

Relative position & motion

Integrate/Differentiate for other parameters

Global Positioning System

Absolute position/location on earth

Local differential error correction

Integrate/Differentiate for other parameters


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Wheel Encoders

Nubotics.com, $27

Jun 98, Oct 2000 Encoder


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Sensors Position/Location

Parallax.com

$80


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Sensors Compass (Orientation)

Track bearing & distance to determine position L: Parallax.com, $30

R: Dinsmoresensors.com, $13-$37


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Sensors Voltage

Passive Senses electric field Fluke Electric Field Sensors

$23

$24

$25

S C t


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Sensors Current

Series measurement with Hall Effect device Current loop (coil), then amplified

Magnetoresistive (Wheatstone bridge)


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Sensors Current


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Sensors Current


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Sensors Chemical

Passive (sensors only)

Active (optical emitter/photo sensor)

Sensors Chemical


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Sensors Chemical Smoke Detectors - Cheap, readily available, $5

Oxygen concentration sensors - CO, H4S, CH4, pricey

See HowStuffWorks.com


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Sensors Conclusion

Sensors provide a way of simulating aliveness

Sensors give robots environmental awareness

Sensors provide of means of human protection

Sensors help robot preserve itself Sensors enable goal seeking

Sensors enable closed-loop interaction

Sensors make robots interesting Sensors can make programming challenging


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Sensors

Q&AComments

Discussion


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Backup Slides

P ll S S l $16


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Parallax Sensor Sampler - $165

Memsic 2125 Accelerometer Sensirion Temperature and Humidity Sensor

Flexiforce Demo Kit

PING))) Ultrasonic Sensor PIR Sensor

Hitachi HM55B Compass Module

Hitachi H48C Tri-Axis Accelerometer Module

Piezo Film Vibra Tab Mass

QTI Sensor (IR Surface Color)

S V d /I f Li k


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Sensor Vendor/Info Links

http://www.dinsmoresensors.comhttp://www.fluke.comhttp://www.howstuffworks.comhttp:// www.lynxmotion.com

http://www.magnetometer.orghttp:// www.nubotics.comhttp:// www.parallax.comhttp://www.raztec.co.nzhttp:// www.robotics.com

http:// www.robotroom.comhttp://www.sensorland.comhttp://www.seattlerobotics.org/encoderhttp:// www solarbotics com

robotic actuators and sensors by MAHENDRA BABU MEKALA OF pbrvits, kavali

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Transcript of robotic actuators and sensors by MAHENDRA BABU MEKALA OF pbrvits, kavali