Transcript Odor Sensors

Sensors
For Robotics
What makes a machine a robot?
Sensing
information
about the
environment
where
is the
truck?
where should I dig?
Planning
Acting
action
on the
environment
Gas Sensor
Gyro
Accelerometer
Pendulum Resistive
Tilt Sensors
Metal Detector
Piezo Bend Sensor
Gieger-Muller
Radiation Sensor
Pyroelectric Detector
UV Detector
Resistive Bend Sensors
Digital Infrared Ranging
CDS Cell
Resistive Light Sensor
Pressure Switch
Miniature Polaroid Sensor
Limit Switch
Touch Switch
Mechanical Tilt Sensors
IR Pin
Diode
IR Sensor w/lens
Thyristor
IR Reflection
Sensor
Magnetic Sensor
Magnetic Reed Switch
IR Amplifier Sensor
Hall Effect
Magnetic Field
Sensors
Polaroid Sensor Board
IRDA Transceiver
Lite-On IR
Remote Receiver
Radio Shack
Remote Receiver
IR Modulator
Receiver
Solar Cell
Compass
Compass
Piezo Ultrasonic Transducers
Why do robots need sensors?
What is the angle of my arm?

internal information
What Is a Sensor?
• Anything that detects the state of the
environment.
• Collect information about the world
• Sensor - an electrical/mechanical/chemical
device that maps an environmental attribute to
a quantitative measurement
• Each sensor is based on a transduction
principle - conversion of energy from one form
to another
What you (and the robot) can do
without sensors?
• Close your eyes. Plug your ears. Hold your nose. Tie your
hands behind your back.
– Shut your mouth. Tie your shoelaces together. Spin yourself around a
few times.
• Now walk. How does it feel? That's exactly what your robot
feels: nothing - without sensors.
• You have been given many types of sensors that can be used
in a variety of ways to give your robot information about the
world around it.
• We will explain each of the sensors you can find in the lab, how
it works, what it's good for, and how to build it.
The simplest possible use of sensors
• The diagram serves to illustrate the general case of
sensing a specific phenomenon.
– In this case it is the presence or absence of light.
• The sensor in this case is a photo-resistor.
– When sufficient light strikes it, its internal resistance is reduced to
several hundred Ohms.
– When no light strikes it its resistance is typically several million
Ohms.
light
Simple and Complex Sensors
• Sensors range from simple to complex in the
amount of information they provide:
 a switch is a simple on/off sensor
 a human retina is a complex sensor
consisting of more than a hundred million
photosensitive elements (rods and cones)
• Sensors provide raw information, which can be
treaded in various ways,
• For example, we can simply react to the
sensor output:
How to detect people?
• For example, how would you
detect people? Some options
include:
 temperature: pyroelectric sensors
detect special temperature ranges
 movement: if everything else is static
 shape: now you need to do complex
vision processing
 color: if people are unique colored in
your environment
How to detect people?
• Let's think about something even more
simple: how would you measure
distance:
 ultrasound sensors give you distance directly
(time of flight)
 infra red through return signal intensity
 two cameras (i.e., stereo) can give you
distance/depth
 a camera can compute it from perspective
 use a laser and a fixed camera, triangulate
 structured light; overlying grid patterns on the
world
 frequency and phase modulation interferometry
Biological Analogs
• All of the sensors we describe in this lecture
exist in biological systems
 Touch/contact sensors with much more
precision and complexity in all species
(spiders?)
 Polarized light sensors in insects and birds
 Bend/resistance receptors in muscles
 and many more...
You have to understand sensors
• we need to make one point very clear:
– Sensors are not magical boxes.
– All information you get from sensors must be decoded
by you, the human builder and programmer.
• Sensors convert information about the
environment into a form that can be used by the
computer.
– The sensors that are on the robot can be related to
sensors found in humans.
You have to understand sensors
• These sensors convert information about the
environment into neural code that your brain can
understand:
– Touch sensors embedded in your skin,
– visual sensors in your retina,
– and hair cells in your ears
• Your brain needs to understand the neural code
before you can react.
– Since you will be programming the robot, you will need
to understand the output of the sensors before you can
program your robot to react to different stimuli.
Types of Sensors
• Active
– send signal into environment and measure
interaction of signal w/ environment
– e.g. radar, sonar
• Passive
– record signals already present in environment
– e.g. video cameras
Types of Sensors
• Classification by medium used
– based on electromagnetic radiation of
various wavelengths
– vibrations in a medium
– concentration of chemicals in
environment
– by physical contact
Types of Sensors
• Exteroceptive: deal w/ external world
– where is something ?
– how does is look ? (camera, laser rangefinder)
• Proprioceptive: deal w/ self
– where are my hands ? (encoders, stretch
receptors)
– am I balanced ? (gyroscopes, INS)
Types of Sensors
• Interoceptive
– what is my thirst level ? (biochemical)
– what is my battery charge ? (voltmeter)
• For the most part we’ll ignore these in this
class
Analog versus Digital
Sensors
• In all our robotics kits the sensors are digital or analog.
• For instance, in HandyBoard, analog sensors can be
plugged into the analog sensor ports, which return
values between 0 and 255.
• Digital sensors can be plugged into either the digital
ports or the analog ports, but will always return either
0 or 1.
ANALOG 0 =< x =< 255
DIGITAL 0 or 1
Analog Sensors and Thresholding
• Analog sensors, such as photo-resistors, can tell you:
– how far the sensor has bent,
– or how much light is hitting the sensor.
• They answer questions with more detail.
– Analog sensors, however can be converted to digital
sensors using thresholding.
• Instead of asking the question “How much is the
sensor bent?” you can ask the question: “Is the sensor
bent more than half way?”
• The threshold can be determined by playing around with the
specific sensor.
Touch sensors
electrical flow
a simple
switch
force
voltage
measurement
Resistive Position Sensors: bending
• We said earlier that a photocell is a
resistive device, i.e., it senses resistance
in response to the light.
• We can also sense resistance in response
to other physical properties, such as
bending.
• These bend sensors were originally
developed for video game control
• They are generally quite useful:
– Video game accessories are in general useful for robotics
and virtual reality and very cheap.
Bend Sensors
You can remove it
from Nintendo
gloves
• Useful for contact sensing and wall-tracking
• The bend sensor is a simple resistance
– As the plastic strip is bent (with the silver rectangles facing
outward), the resistance increases
Bend sensor
a variable
resistor
resistance changes
as it bends
V=IxR
assuming constant
current, the measured
voltage changes with
resistance
Applications of Resistive Analog
Sensor
Sensors
Measure bend of a joint
Sensors
Wall Following/Collision
Detection
Sensor
Weight Sensor
Inputs for Resistive Sensors
V1
Voltage divider:
R1
You have two resisters, one
V
is fixed and the other varies,
as well as a constant voltageR2
V2
V1 – V2 * (R2/R1+R2) = V
Known unknown measure
micro
Analog to Digital
(pull down)
micro
Single Pin
Resistance
Measurement
+
-
Binary
Threshold
Comparator: if
voltage at + is greater
than at -, high value out
Potentiometer
another
rotational sensor
R
resistance changes
with position
of dial
Potentiometer: the main ideas
• Potentiometers are very common for manual tuning; you know them
from some controls (such as volume and tone on stereos).
• Typically called pots, they allow the user to manually adjust the resistance.
• The general idea is that the device consists of a movable tap along two fixed
ends.
• As the tap is moved, the resistance changes.
• As you can imagine, the resistance between the two ends is fixed, but the
resistance between the movable part and either end varies as the part is
moved.
• In robotics, pots are commonly used to sense and tune position for sliding
and rotating mechanisms.
Potentiometers
•Mechanical varieties:
– Linear and rotational styles - make position
sensors for both sliding mechanisms and
rotating shafts
– Resistance between the end taps is fixed, but
the resistance between either end tap and the
center swipe varies based on the position of the
swipe
• Electrical varieties:
– Linear taper - linear relationship between
position and resistance. Turn the pot 1/4 way,
the resistance between the nearer end and the
center is 1/4 of end-to-end resistance
– Audio taper - logarithmic relationship between
position and resistance. At one end, 1/4 turn
would swipe over a small bit of total resistance
range, while at the other end, 1/4 turn would be
most of the range
Figure 5.5:
Potentiometer
Assemblies
•
•
Kits contain several sizes of
potentiometers, also known
as variable resistors.
Potentiometers should be
wired with Vcc and ground
on the two outside pins, and
the signal wire on the center
tap.
–
This will, in effect, place the
resistance of the
potentiometer in parallel
with the 47K pull-up on the
expansion board and is
more stable than just using
one side and the center tab
to make a plain variable
resistor
Various uses of Potentiometers
• Potentiometers have a variety of uses:
– In the past, they have been used for
menuing programs
– For angle measurement for various rotating
limbs
– For scanning beacons.
• They can be used with a motor to mimic
servos, but that's a difficult task.
– It is important to notice that the pots are not
designed to turn more than about 270
degrees.
– Forcing them farther is likely to break them.
Linear Potentiometers and
their use in HandyBoard
• A linear potentiometer can be used to measure
precise linear motion,
– such as a gate closing,
– or a cocking mechanism for ring balls or blocks.
• Frob-knob
– The frob knob is the small white dial on the lower
left corner of the Expansion Board.
• It returns values between 0 and 255 and
provides a handy user input for adjusting
parameters on the y or for menuing routines to
select different programs.
Encoders
Encoders measure rotational motion.
They can be used to measure the rotation
of a wheel.
Servo motors: Used in conjunction with
an electric motor to measure the motor’s
position and, in turn, control its position.
Encoders
Voltage square wave
on
on
off
off
1
2
off
3
4 ...
Important spec:
Number of counts
per revolution
Encoder
• Incremental encoder
– usually requires 2 sensors to determine speed
and direction
• Technology
– magnet + hall sensors (incremental)
– optical sensors with black/white segments
(incremental)
Encoder
• Encoder signal (2 lines) are connected to microcontroller like 2 binary sensors
(digital input lines)
• Microcontrollers usually have special internal registers for pulse counting
 ⇒ This is done in parallel to normal calculations
 Does not slow down the cpu
Sensors Based on Sound
• SONAR: Sound Navigation and Ranging
– bounce sound off of something
– measure time for reflection to be heard - gives a range
measurement
– measure change in frequency - gives the relative speed
of the object (Doppler effect)
– bats and dolphins use it with amazing results
– robots use it w/ less than amazing results
Sonar and IR Proxmity
Odor Sensors
• Detection of chemical compounds and
their density in an area
– spectroscopy - mostly lab restricted
– fibre-optic techniques - recently developed
– chemical detection - sniffers aand electronic
noses via “wet chemistry on a chip”
• No major penetration in robotics yet
applications are vast (e.g. mine detection)