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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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Increased Resolution
More teeth on rotor or stator
Half stepping
S
S
N
N
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Increased Resolution
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
Relative position- direction- resolution
gratinglight emitter
light sensor
decode
circuitry
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Optical Encoders
Relative position- direction- resolution
gratinglight emitter
light sensor
decode
circuitry
A
B
A
B
A lags B
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Optical Encoders
Relative position- direction- resolution
gratinglight emitter
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