Laser application, vision application, sonar application and sensor fusion (6wasserf@informatik.uni-hamburg.de)
Outline Introduction Mobile robots perception Definitions Sensor classification Sensor Performance A closer look at Ultrasonic sensors Laser rangefinders Vision technology Sensor Fusion
Outline Introduction Mobile robots perception Definitions Sensor classification Sensor Performance A closer look at Ultrasonic sensors Laser rangefinders Vision technology Sensor Fusion
Introduction Mobile robots perception A robot without perception is not a robot To make reasonable assumptions as basis for its decisions, a robot must be able to observe its environment This must be done using a number of sensors
Introduction Sensor classification Lots of different sensors exist...
Introduction Sensor classification...to measure lots of values: -... temperature sound amplitude battery voltage distance light intensity wheel load position air-pressure motor speed orientation physical contact wheel position speed...
Introduction Sensor classification proprioceptive exteroceptive active passive
Introduction Sensor classification proprioceptive exteroceptive active wheel/motor sensors: - optical encoders, - magnetic encoders, - inductive encoders, -... - ultrasonic sensors, - laser rangefinder, - doppler radar, - GPS passive - gyroscopes, - potentiometers, - brush encoders - compass, - CCD/CMOS cameras
Sensor performance Basic sensor performance Dynamic range Resolution Frequency In situ sensor performance Sensitivity / cross sensitivity Systematic error Random error Precision / accuracy
Sensor performance Basic sensor performance Dynamic range Ratio between lower and upper limits of input values to the sensor Resolution Frequency In situ sensor performance Sensitivity / cross sensitivity Systematic error Random error Precision / accuracy
Sensor performance Basic sensor performance Dynamic range Ratio between lower and upper limits of input values to the sensor Resolution Minimum difference between two values that can be detected by a sensor Frequency In situ sensor performance Sensitivity / cross sensitivity Systematic error Random error Precision / accuracy
Sensor performance Basic sensor performance Dynamic range Ratio between lower and upper limits of input values to the sensor Resolution Minimum difference between two values that can be detected by a sensor Frequency Speed with which a sensor can provide a stream of readings In situ sensor performance Sensitivity / cross sensitivity Systematic error Random error Precision / accuracy
Outline Introduction Mobile robots perception Definitions Sensor classification Sensor Performance A closer look at Ultrasonic sensors Laser rangefinders Vision technology Sensor Fusion
Ultrasonic sensor d =c t d c t = distance travelled (rtt) = speed of wave propagation = time of flight
Ultrasonic sensor Advantages Ultrasonic sensors are: Very cheap Independent from external signals Usable without complex preprocessing Used in almost every mobile robot
Ultrasonic sensor Disadvantages / Problems Sensor measures regions of constant depth instead of points Low frequency Mean distance to object = 3m Wave speed ~ 434 m/s 20 ms per value Imagine 20 sensors around the robot, measuring sequentially to minimize interference... frequency = 2.5 Hz
Ultrasonic sensor Disadvantages / Problems Threshold: triggering incoming sound wave as valid echo Acoustically reflective material Reflection on surfaces angled with respect to the face of the sensor
Laser rangefinder 3 ways to measure time-of-flight: Pulsed laser Frequency modulated continuous waves Phase shift measurement
Laser rangefinder Phase-shift measurement Sensor transmits amplitude modulated light Known modulation frequency (e.g. 5 MHz)
Laser rangefinder Phase-shift measurement Sensor transmits amplitude modulated light Known modulation frequency (e.g. 5 MHz) Measuring of the phase-shift between transmitted and reflected signal Computing the distance using c = f c = speed of light f = modulating frequency = wavelength of the modulation
Laser rangefinder
Laser rangefinder Advantages High frequency Again: mean distance to object = 3m Wave speed ~ 300.000 km/s 0.00002 ms per value Theoretical frequency ~ 50 MHz Sensor measures points instead of regions
Laser rangefinder Disadvantages / Problems Expensive Reflection of the laser-beam on highly polished surfaces Cannot detect transparent materials (glass)
Vision technology Vision is the most powerful sense Provides a machine with the same information as a human uses for interaction with the environment It is a long way from raw-data to useful information
Vision technology Sensors CCD (charged coupled device) CMOS (complementary metal oxide semiconductor)
Vision technology Sensors CCD CCD (charged coupled device) CMOS (complementary metal oxide semiconductor)
Vision technology Sensors CMOS CCD (charged coupled device) CMOS (complementary metal oxide semiconductor) z
Vision technology visual ranging Depth is a very important information in mobile robotics applications Any vision chip collapses 3D world to a 2D image Additional information is needed: Stereo vision Motion Changing the cameras geometry
Vision technology visual ranging Depth from focus Depth from stereo vision
Vision technology visual ranging Depth from focus 1 1 1 = f d e Depth from stereo vision
Vision technology visual ranging Depth from focus Depth from stereo vision
Outline Introduction Mobile robots perception Definitions Sensor classification Sensor Performance A closer look at Ultrasonic sensors Laser rangefinders Vision technology Sensor Fusion
Sensor fusion Every sensor has different advantages / disadvantages Different sensors for different aspects of one task sensor fusion
Sensor fusion
Sensor fusion
Sensor fusion
Sensor fusion Thank you for your attention!