Sensors and Sensing
for Reactive Robots
Alexander Stoytchev
Mobile Robot Lab
Georgia Tech
Sensing: Conceptual Level
Sensor Classification
• Proprioception
– relative to internal frame of reference
• Exteroception
– measurements of the environment relative to
robot’s frame of reference
• Exproprioception
– Measurement of the position of robot body or
parts relative to the layout of the environment
Proprioceptive Sensors
• Shaft Encoders
• Internal Navigation System (INS)
• Global Positioning System (GPS)
– Regular
– Differential GPS (stationary base + moving robot)
Proximity Sensors
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Sonar
IR
Bumpers
Radar
Laser Range Finders
– Time of Flight
– Phase-based
Other Sensors
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Compass
Accelerometers
Inclinometers
Gyroscopes
Thermometers
Microphones
Cameras
Sensor Properties
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Field of view (FOV)
Update rate
Accuracy/Repeatability/Resolution
Applicability to target domain
Power consumption
Hardware reliability
Size
Computational requirements
Interpretation reliability
Desired Sensor Properties
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Simple to operate and maintain
Modular
Redundant (physical & logical redundancy)
Fault Toloerant
Cheap!
Sensor Errors
• False Positive
• False Negative
• Sometimes not clear
• Cost of Errors
Case Study: Sonar
• Calculate distance based on the time of flight
d=½ct
c = c0 + 0.6 T
c0 = 331 m/s T- temperature in degrees Celsius
• Frequency – 50 KHz
Sonar Cone Regions
Problems with Sonars
Sensing: Conceptual Level
Raw v.s. Logical Sensors
• Raw Sensor Data
– List of distances to obstacles
• Logical Sensor Data
– Egocentric polar/Carthesian coordinates
– Independent of physical sensor
Passive v.s Active Sensors
• Passive – the environment provides the
medium for observation
• Active – the sensor puts out an energy into
the environment
• != Active Sensing - use an effector to better
position a sensor for observation
Sensor Fusion
Sensor Fission
Sensor Fashion