Sensing

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Sensing

  1. 1. OVERVIEW OFOVERVIEW OF OUR SENSORSOUR SENSORS FORFOR ROBOTICSROBOTICS
  2. 2. What makes a machine a robot?What makes a machine a robot? where should I dig? where is the truck? Sensing Planning Acting information about the environment action on the environment
  3. 3. Why do robots need sensors? θ? internal information What is the angle of my arm?
  4. 4. What is Sensing ?  Collect information about the world  Sensor - an electrical/mechanical/chemical device that maps an environmental attribute to a quantitative measurement  attribute mixtures - often no one to one map  hidden state in environment  Each sensor is based on a transduction principle - conversion of energy from one form to another  Also known as transducers
  5. 5. Why do robots need sensors? Where am I? localization ?
  6. 6. Why do robots need sensors? Will I hit anything? obstacle detection
  7. 7. Sensing for specific tasks Where is the cropline? Autonomous harvesting
  8. 8. Sensing for specific tasks Autonomous material handling Where are the forkholes?
  9. 9. Sensing for specific tasks Where is the face? Face detection & tracking
  10. 10. Types of SensorsTypes 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
  11. 11. 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
  12. 12. 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)
  13. 13. 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
  14. 14. Simple Practical SensorsSimple Practical Sensors that we can purchasethat we can purchase Touch sensors Tilt sensors Encoders Bend sensors Light sensors Temperature sensors Potentiometers Laser rangefinders Cameras
  15. 15. Touch sensors force voltage measurement electrical flow a simple switch
  16. 16. Tilt sensors another simple switch gravity
  17. 17. EncodersEncoders 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.
  18. 18. Encoders Important spec: Number of counts per revolution Voltage square wave on on offoffoff 1 2 3 4 ...
  19. 19. Sample problems Sensor Analysis How far does the wheel travel for 1 encoder count? What happens if we change the wheel diameter? How many counts are there per meter of travel? 16 counts per rev. 10 cm wheel diameter 10 cm
  20. 20. Sample problems Diameter Circumference C = πD C = 10π cm 10π cm 1 rev = 1 rev 16 counts x 1.96 cm count
  21. 21. Sample problems Suppose I want 1.0 cm / count. What should my wheel diameter be? 1.0 cm count =1 rev 16 counts x 16 cm rev C = 16 cm D = C π = 16 π =5.09 cm
  22. 22. Sample problems For my 10 cm wheel, how many encoder counts will there be for 1 meter of travel? 1.96 cm count = 100 cm 1 meter x 0.0196 m count = 0.0196 m/ct 1 51 counts/m
  23. 23. Physics 101 Ohm’s Law V = I x R V RI voltage resistancecurrent 9 = 0.009 x 1000 (9 Volts) (1000 Ohms) (0.009 Amps)
  24. 24. Electrical analogy Voltage Current Resistance a larger pipe is less resistance so more water a smaller pipe is more resistance so less water
  25. 25. Bend sensor a variable resistor resistance changes as it bends V = I x R assuming constant current, the measured voltage changes with resistance
  26. 26. Light sensor photo-resistor resistance changes with light intensity
  27. 27. Temperature sensor thermal resistor “thermistor” resistance changes with temperature
  28. 28. Potentiometer another rotational sensor resistance changes with position of dial R
  29. 29. Sample problem Bend sensor specs: 100 Ω when straight 1000 Ω when bent Given a 5 V source, what is the min. and max. current that is drawn? V = I x R I = V R min = 5 1000 = 5 mA max = 5 100 = 50 mA
  30. 30. Sensors Based on EM SpectrumSensors Based on EM Spectrum  Basically used for ranging  Light sensitive  eyes, cameras, photocells etc.  Operating principle  CCD - charge coupled devices  photoelectric effect  IR sensitive - FLIR  sense heat differences and construct images  night vision application
  31. 31. EM Spectrum  Radio and Microwave  RADAR: Radio Detection and Ranging  Microwave radar: insensitive to clouds  Coherent light  all photons have same phase and wavelength  LASER: Light Amplification by Stimulated Emission of Radiation  LASER RADAR: LADAR - accurate ranging
  32. 32. The SICK Laser Rangefinder
  33. 33. EM Spectrum  Nuclear Magnetic Resonance (NMR)  heavy duty magnetic field lines up lines up atoms in a body  now expose body to radio signals  different nuclei resonate at different frequencies which can be measured leading to an image
  34. 34. Local Proximity Sensing in EM  Infrared LEDs  cheap, active sensing  usually low resolution - normally used for presence/absence of obstacles rather than ranging  operate over small range
  35. 35. Sensors Based on SoundSensors 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
  36. 36. Sonar and IR Proxmity
  37. 37. Odor SensorsOdor 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)
  38. 38. Touch SensorsTouch Sensors  Whiskers, bumpers etc.  mechanical contact leads to  closing/opening of a switch  change in resistance of some element  change in capacitance of some element  change in spring tension  ...
  39. 39. Proprioceptive SensorsProprioceptive Sensors  Encoders, Potentiometers  measure angle of turn via change in resistance or by counting optical pulses  Gyroscopes  measure rate of change of angles  fiber-optic (newer, better), magnetic (older)  Compass  measure which way is north  GPS: measure location relative to globe
  40. 40. Propriceptive Sensors
  41. 41. Problem: SensorProblem: Sensor ChoiceChoice  What sensors to employ ?  E.g. mapping  ranging - laser, sonar, IR, stereo camera pair  salient feature detection - doors using color  Factors  accuracy, cost, information needed etc etc.
  42. 42. Problem: SensorProblem: Sensor PlacementPlacement  Where do you put them ?  On/off board (e.g. localization using odometry vs. localization using beacons)  If onboard - where ?  Reasonable arrangements - heuristic  Optimal arrangements - mathematically rigorous
  43. 43. References  Photo’s ,Text and Schematics Information  www.acroname.com  www.lynxmotion.com  www.drrobot.com  Alan Stewart • Dr. Gaurav Sukhatme • Thomas Braunl • Students 2002, class 479
  44. 44. Questions to students 1. How would you apply Tilt Sensors in a walking robot? 2. List and explain all applications of Encoders 3. Light sensors in a mobile robot. Describe fusion, mapping and how to control motors. 4. Temperature sensors in robotics. 5. List sensors based on electromagnetic spectrum. 6. Laser rangers 7. Odor sensors in mobile robots. Show one good application. In each of the above problems think about sensor placement, how many of them, fusion, mapping and how used to control. 8. Sonars 9. Gyroscopes and compases in a mobile robot. 10. Describe your idea of using a GPS sensor in a mobile robot. Discuss accuracy, how connected. What application of the robot?

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