Robot sensors A robot can be defined as an intelligent link between - PowerPoint PPT Presentation

Robot sensors • A robot can be defined as an intelligent link between perception and action Robot Action Perception Environment www.biorobotics.ttu.ee

For a mobile robot Knowledge, Mission Data Base Commands Cognition Localization "Position" Path Planning Map Building Global Map Environment Model Path Local Map Information Path Motion Control Extraction Execution Perception Raw data Actuator Commands Sensing Acting Real World Environment 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Sensors of the SCI TOS G5 robot Camera Microphones Laser range finder Emergency stop button Sonar sensors Wheel encoders Bumper www.biorobotics.ttu.ee

Robot sensors Robart II, H.R. Everett 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Sensor classification • Proprioceptive sensors •measure values internally to the system (robot), •e.g. motor speed, wheel load, heading of the robot, battery status • Exteroceptive sensors •information from the robots environment •distances to objects, intensity of the ambient light, unique features. www.biorobotics.ttu.ee

Sensor classification • Passive sensors •energy coming for the environment • Active sensors •emit energy and measure the reaction www.biorobotics.ttu.ee

Sensor classification www.biorobotics.ttu.ee

Sensor classification www.biorobotics.ttu.ee

Sensor performance • Dynamic range •ratio between lower and upper limits, usually in decibels • Range •upper limit • Resolution •minimum difference between two values www.biorobotics.ttu.ee

Sensor performance • Linearity •variation of output signal as function of the input signal • Bandwidth or Frequency •the speed with which a sensor can provide a stream of readings • Sensitivity •ratio of output change to input change www.biorobotics.ttu.ee

Sensor performance • Cross-sensitivity •sensitivity to environmental parameters that are orthogonal to the target parameters • Error / Accuracy •difference between the sensor’s output and the true value www.biorobotics.ttu.ee

Sensor performance • Systematic error • deterministic errors •caused by factors that can (in theory) be modeled and predicted • Random error • non-deterministic • cannot be modelled but can be described probabilistically • Precision •reproducibility of sensor results www.biorobotics.ttu.ee

Wheel encoders Measure the position or speed of the wheels 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Measuring travelled distances Dead-reckoning (deduced reckoning) – determining the present location of a vessel from some previous position through known course and velocity information over a given lenth of time Odometry – the course and path length information is directly derived from on board odometer (e.g. optical wheel encoders) www.biorobotics.ttu.ee

Heading sensors • Used to determine the robots orientation and inclination. • Together with the velocity estimates produce dead- reckoning information • Compasses • I nclinometer Gyro •Mechanical gyros •Optical gyros www.biorobotics.ttu.ee

Beacons • Beacons are signaling guiding devices with a precisely known position • Natural beacons (landmarks) • Artificial beacons (radio transmitters, reflectors) • Active and passive beacons • Require the environment to be prepared and changed for the robot 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Global Positioning System 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Range sensors •Range information is the key element for localisation and environment modelling •Ultrasonic sensors- measure speed of sound •Laser range sensors – measure speed of electomagnetic waves d = c t Where d = distance traveled (usually round-trip) c = speed of wave propagation t = time of flight. www.biorobotics.ttu.ee

Ultrasonic sensors transmit a packet of sound waves distance d of the echoing object can be calculated based on the propagation speed of sound c and the time of flight t. ct d = 2 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Ultrasonic sensors measurement cone 0° -30° 30° -60° 60° Amplitude [dB] 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Signal reflection and absorbtion 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Laser rangefinders •Transmits and receives laser light •Measures the phase shift of the reflected light D Transmitter P Target L Phase Transmitted Beam Measurement Reflected Beam 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 www.biorobotics.ttu.ee

Laser rangefinders Amplitude [V] Phase [m] θ 0 Transmitted Beam λ Reflected Beam 1. R. Siegwart, I. Nourbakhsh, "Introduction to Autonomous Mobile Robots", The MIT Press,2004 θλ θλ = = + = + D D ' L 2 D L π π 2 2 www.biorobotics.ttu.ee

Perception with a sonar www.biorobotics.ttu.ee

Perceptions with a laser www.biorobotics.ttu.ee

Mapping with a laser rangefiner www.biorobotics.ttu.ee

Mapping with a laser rangefiner www.biorobotics.ttu.ee

Home assignment: odometry • Drive around in the simulator with the SCITOS robot and compare the real position of the robot to the position estimated by odometry readings • Observe how do the errors accumulate, what are the maneuvers that more increase the odometry error? www.biorobotics.ttu.ee

Home assignment: laser and sensor readings • Drive around in the simulator with the SCITOS robot and compare laser and sonar readings. • Explain how the sensor readings are different www.biorobotics.ttu.ee