lecture3 sensors short.ppt - university of southern …csci545/slides/lecture3_sensors_short.pdf ·...

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Sensors

CSCI545Introduction to Robotics

Hadi Moradi

Previous LectureDC motorsDC motors

InefficientOperating voltageOperating currentStall currentStall torqueStall torqueGearing up and downGear ratiosPWMServo motors vs. stepper motors

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SensorsPerception through sensorsPerception through sensors

Contact: bump, switch

Distance: Ultrasound, radar, infra red

Light level: photo cells, cameras

Sound level: microphone


Strain: strain gauge

Rotation: encoders

Magnetism: compasses

Smell: chemical

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Temperature: thermal, infra red

Inclination: inclinometers, gyroscopes

Pressure: pressure gaugesPressure: pressure gauges

Altitude: altimeters…

SensorsSimple complexSimple complex

Contact switch human retina

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The General QuestionGiven the sensory reading what was theGiven the sensory reading what was the world like?

Example: SkinExample: Skin

Levels of ProcessingA switch:

open = 0 voltsClosed = 5 volts

A digital scale:

Microphone:Microphone:

Camera:

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ProprioceptionSensing informationSensing information

Proprioception:

Exteroception:Examples of proprioception

Sensor FusionCombining multiple sensorsCombining multiple sensors Difficulties:

E l H b iExample: Human brain

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Magnetic Field Sensor of Baby Loggerhead Sea Turtles

Field Inclination AngleField IntensityNeuron sensors in the brain?

http://news.nationalgeographic.com/news/2001/10/1012_TVanimalnavigation.html

http://faculty.washington.edu/chudler/magtur.html

Magnetic Field Sensor of Baby Loggerhead Sea Turtles

http://www.unc.edu/depts/oceanweb/turtles/

Research by Dr. Kenneth Lohmann

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Ohm’s Law

V= IRV= IRV =voltage (volts)I =current (Amps)R = resistance (Ohms)

Switch SensorsOpen vs closedOpen vs. closed

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Light SensorsA variable resistorA variable resistor that changes based on the light.Brighter light =>

low resistancelow resistancedarker light =>

Higher resistance

The Importance of shielding

Note: Shielding, position, and directionality of the photocells are important.

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Resistive Position SensorsOriginallyOriginally developed for video game control.

Bend Sensor

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PotentiometersVolume control in your stereoVolume control in your stereoTypically called pots

Example

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Example

Reflective Opto-sensorsEmitter and detectorEmitter and detector Emitter:

LED

Detector:PhotodiodePhotodiodePhototransistor

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Photodiode vs. PhotoresistorPhotoresistor:Photoresistor:Photodiode/phototransistor:

Phototransistor vs. Photodiode:

Applicationsobject presence detectionobject presence detection object distance detection surface feature detection (finding/following markers/tape) wall/boundary trackingwall/boundary tracking rotational shaft encoding

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Sensor limitationsLight reflectivity:g y

Surface color

TextureAmbient light: How to overcome the ambient light?

Sensor calibration

=> Partially observable

Break Beam Sensors

Any pair of compatible emitter-detector devices can be used to make a break-beam sensorExamples:

Where have you seen these?

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Shaft EncodingMeasure angular rotationMeasure angular rotation

Example:Speedometer: speed of rotationp pOdometer: number of rotations

Q: What happens if there is only one notch in the disk?

An Example

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Quadrature Shaft Encoder

Clockwise rotation signal

Output Signal

ccwcw

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Modulation and Demodulation of Light

Problem: Ambient lightProblem: Ambient lightSolution:

Example: Home remote controlUsage:g

Modulation and Demodulation of Light

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Proximity SensingThe distance to a nearby objectThe distance to a nearby object

Just the return of signal

Distance Sensing

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Infra Red (IR) SensorsInfra red part of the spectrumInfra red part of the spectrumUsed like break beam and reflectance sensorsAdvantage

Time of FlightEmitter: send aEmitter: send a chirpCollector: Receives the bounce backElapsed time

1.12 feet/ms

Called echolocation

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Bats

Man Made ExampleUsed to mapUsed to map undersea surface

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Undersea Mapping

Picture from Bluefin Robotics

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Problem 1: Multiple ReflectionsWhich reflectionWhich reflection gets back earlier?Which reflection should be used for calculation?

Object 2

Object 1

Sonar

Problem 2: Specular ReflectionGraze the surfaceGraze the surface and bounce off

Object 2

Object 1

Sonar

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Problems

Other Usages: NavBelt

http://www.engin.umich.edu/research/mrl/00MoRob_19.html

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Navchair

http://www.engin.umich.edu/research/mrl/00MoRob_19.html

GuideCane

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GuideCane

Machine VisionMachine VisionProblem: determine the objects in theProblem: determine the objects in the environment (Understand the environment).Example: RoboCup

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The Physics of VisionThe Physics of Vision

Light goes through the irisImpinges retina

Camera Light ProcessingCamera Light Processing

A very simple processing: convert the image to a normal image

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Image ReconstructionImage Reconstruction

Reconstruction: what was the world likeReconstruction: what was the world like that produced this image?

Pixelizing the Image PlanePixelizing the Image Plane

pixels: picture cellspixels: picture cellsEach picture divided into small cells

Typical camera: 512 X 512 pixels Human eye:

120 x 10^6 rods120 x 10^6 rods 6 x 10^6 cones

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Image BrightnessImage Brightness

B i h i l h fBrightness: proportional to the amount of light directed toward the cameraBrightness depends on:

Patch BrightnessPatch Brightness

Th b i h d dThe brightness depends on:specular (bounce off the surface)diffuse (re-emitted)

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First Steps of Early VisionFirst Steps of Early VisionExample:Example:

b&w camera 512 x 512 pixel image plane. intensity level between white and black

Question:Do we know if there is an object?Do we know if there is an object? How do we find an object in the image?

An ExampleAn Example

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Edge DetectionEdge DetectionEdges: curves in the image plane with significant change in the brightness levelA simple approach: to look for sharp brightness changes:

Problem:

Example: Human Body ProjectExample: Human Body Project

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Smoothing of NoiseSmoothing of NoiseNoise: Small picks in differentiated imageNoise: Small picks in differentiated image.Eliminating noise:

Finding ObjectsFinding Objects

Step 2: Find objects among all those edgesStep 2: Find objects among all those edges. Segmentation:

Q tiQuestions:How do we know which lines correspond to which objects, What makes an object?

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Finding ObjectsFinding ObjectsUse clues to detectUse clues to detect objects. The math is hard...

Clues for Segmentation (1)Clues for Segmentation (1)

Use stored models (model-based vision)Use stored models (model based vision)

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Clues for Segmentation (1)Clues for Segmentation (1)

MAKRO 1.1 drives to a T-shaped junction, measures its width, drives back, performs a turn, stops, drives back and performs a turn back into the main pipe. Second run, different point of view

Clues for Segmentation(2)Clues for Segmentation(2)

Use motion (motion vision)Use motion (motion vision)

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Use binocular stereopsisUse binocular stereopsis(stereo vision)


Left image Right image

Image after disparity

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Use textureUse texture

Use shadingshading, contours,Use shadingshading, contours, …recover shape in a similar way as from texture

Complexity of Vision SensingComplexity of Vision Sensing

Reconstruction:Reconstruction:

If no need for reconstruction:Si lif i i iSimplify vision processing

Q: What are some ways of doing that?

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Simplifying VisionSimplifying VisionUse color

Use a smaller image plane (e.g., a line)

Use other sensors to complement visionUse other sensors to complement vision

Use task-specific information

Question: Determine the object in this image

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Structured Light VisionStructured Light VisionProject a light on aProject a light on a mirror and scan the area.You may avoid rotating motor and scan with a fullscan with a full surface.

Images courtesy of http://www.caligari.com/

Structured Light VisionStructured Light VisionAny object in theAny object in the environment cuts the light.


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Structured Light VisionStructured Light Vision

A) The whole scene, B) The object w/o laser light, C) the difference


Structured Light VisionStructured Light VisionY= projection of theY= projection of the laser on the image planeH= height of the cameraQuestion: How do you calculate r?


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