Sensors CSCI545 Introduction to Robotics Hadi Moradi Previous Lecture � DC motors � DC motors � Inefficient � Operating voltage � Operating current � Stall current � Stall torque � Stall torque � Gearing up and down � Gear ratios � PWM � Servo motors vs. stepper motors 1
Sensors � Perception through sensors � Perception through sensors � Contact: bump, switch � Distance: Ultrasound, radar, infra red � Light level: photo cells, cameras � Sound level: microphone Sensors � Perception through sensors Perception through sensors � Strain: strain gauge � Rotation: encoders � Magnetism: compasses � Smell: chemical 2
Sensors � Perception through sensors � Perception through sensors � Temperature: thermal, infra red � Inclination: inclinometers, gyroscopes � Pressure: pressure gauges Pressure: pressure gauges � Altitude: altimeters � … Sensors � Simple Simple complex complex � Contact switch human retina 3
The General Question � Given the sensory reading what was the Given the sensory reading what was the world like? � Example: Skin � Example: Skin Levels of Processing � A switch: � open = 0 volts � Closed = 5 volts � A digital scale: � Microphone: Microphone: � Camera: 4
Proprioception � Sensing information � Sensing information � Proprioception: � Exteroception: � Examples of proprioception Sensor Fusion � Combining multiple sensors Combining multiple sensors � Difficulties: � Example: Human brain E l H b i 5
Magnetic Field Sensor of Baby Loggerhead Sea Turtles Field Inclination Angle � Field Intensity � Neuron sensors in the brain? � http://faculty.washington.edu /chudler/magtur.html http://news.nationalgeographic.com/news/ 2001/10/1012_TVanimalnavigation.html Magnetic Field Sensor of Baby Loggerhead Sea Turtles http://www.unc.edu/depts/oceanweb/turtles/ Research by Dr. Kenneth Lohmann 6
Ohm ’ s Law � V= IR V= IR � V = voltage (volts) � I = current (Amps) � R = resistance (Ohms) Switch Sensors � Open vs. closed Open vs closed 7
Light Sensors � A variable resistor A variable resistor that changes based on the light. Brighter light = > low resistance low resistance darker light = > Higher resistance The Importance of shielding � Note: Shielding, position, and directionality of the photocells are important. 8
Resistive Position Sensors � Originally Originally developed for video game control. Bend Sensor 9
Potentiometers � Volume control in your stereo Volume control in your stereo � Typically called pots Example 10
Example Reflective Opto-sensors � Emitter and detector Emitter and detector � Emitter: � LED � Detector: � Photodiode � Photodiode � Phototransistor 11
Photodiode vs. Photoresistor � Photoresistor: Photoresistor: � Photodiode/phototransistor: � Phototransistor vs. Photodiode: Applications � object presence detection object presence detection � object distance detection � surface feature detection (finding/following markers/tape) � wall/boundary tracking � wall/boundary tracking � rotational shaft encoding 12
Sensor limitations � Light reflectivity: g y � Surface color � Texture � Ambient 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 sensor Examples: � Where have you seen these? � 13
Shaft Encoding � Measure angular rotation � Measure angular rotation � Example: � Speedometer: speed of rotation p p � Odometer: number of rotations � Q: What happens if there is only one notch in the disk? An Example 14
Quadrature Shaft Encoder � Clockwise rotation signal Output Signal cw ccw 15
Modulation and Demodulation of Light � Problem: Ambient light � Problem: Ambient light � Solution: � Example: Home remote control � Usage: g Modulation and Demodulation of Light 16
Proximity Sensing � The distance to a nearby object � The distance to a nearby object � Just the return of signal Distance Sensing 17
Infra Red (IR) Sensors � Infra red part of the spectrum Infra red part of the spectrum � Used like break beam and reflectance sensors � Advantage Time of Flight � Emitter: send a Emitter: send a chirp � Collector: Receives the bounce back � Elapsed time � 1.12 feet/ms � Called echolocation 18
Bats Man Made Example � Used to map Used to map undersea surface 19
Undersea Mapping Picture from Bluefin Robotics 20
Problem 1: Multiple Reflections � Which reflection Which reflection gets back earlier? Object 2 � Which reflection should be used for calculation? Object 1 Sonar Problem 2: Specular Reflection � Graze the surface Graze the surface and bounce off Object 2 Object 1 Sonar 21
Problems Other Usages: NavBelt http://www.engin.umich.edu/research/mrl/00MoRob_19.html 22
Navchair http://www.engin.umich.edu/research/mrl/00MoRob_19.html GuideCane 23
GuideCane Machine Vision Machine Vision � Problem: determine the objects in the � Problem: determine the objects in the environment (Understand the environment). � Example: RoboCup 24
The Physics of Vision The Physics of Vision � Light goes through the iris � Impinges retina Camera Light Processing Camera Light Processing A very simple processing: convert the image to a normal image 25
Image Reconstruction Image Reconstruction � Reconstruction: what was the world like � Reconstruction: what was the world like that produced this image? � Pixelizing the Image Plane Pixelizing the Image Plane � pixels: picture cells pixels: picture cells � Each picture divided into small cells � Typical camera: 512 X 512 pixels � Human eye: � 120 x 10^ 6 rods 120 x 10^ 6 rods � 6 x 10^ 6 cones 26
Image Brightness Image Brightness � Brightness: proportional to the amount of B i h i l h f light directed toward the camera � Brightness depends on: � Patch Brightness Patch Brightness � The brightness depends on: Th b i h d d � specular (bounce off the surface) � diffuse (re-emitted) � 27
First Steps of Early Vision First Steps of Early Vision � Example: � 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 Example An Example 28
Edge Detection Edge Detection � Edges: curves in the image plane with significant change in the brightness level � A simple approach: to look for sharp brightness changes: � Problem: Example: Human Body Project Example: Human Body Project 29
Smoothing of Noise Smoothing of Noise � Noise: Small picks in differentiated image � Noise: Small picks in differentiated image. � Eliminating noise: � Finding Objects Finding Objects � Step 2: Find objects among all those edges. Step 2: Find objects among all those edges � Segmentation: � Questions: Q ti � How do we know which lines correspond to which objects, � What makes an object? � 30
Finding Objects Finding Objects � Use clues to detect � Use 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) � 31
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) � 32
Clues for Segmentation(3) Clues for Segmentation(3) � Use binocular stereopsis Use binocular stereopsis (stereo vision) � Clues for Segmentation(4) Clues for Segmentation(4) Left image Right image Image after disparity 33
Clues for Segmentation(5) Clues for Segmentation(5) � Use texture Use texture � Use shading � Use shading shading, contours, shading, contours, … � recover shape in a similar way as from texture Complexity of Vision Sensing Complexity of Vision Sensing � Reconstruction: Reconstruction: � If no need for reconstruction: � Simplify vision processing Si lif i i i � Q: What are some ways of doing that? 34
Simplifying Vision Simplifying Vision Use color � � Use a smaller image plane (e.g., a line) � Use other sensors to complement vision � Use other sensors to complement vision � Use task-specific information Question: Determine the object in this image 35
Structured Light Vision Structured Light Vision � Project a light on a � Project a light on a mirror and scan the area. � You may avoid rotating motor and scan with a full scan with a full surface. Images courtesy of http://www.caligari.com/ Structured Light Vision Structured Light Vision � Any object in the � Any object in the environment cuts the light. Images courtesy of http://www.caligari.com/ 36
Recommend
More recommend
