week 2 Flashcards
what is a signal?
a time-varying value
actions of robots are signals
what is a system in reference to robotics?
something which transforms signals
what is measurement range?
the set of values that can be measured using a measuring instrument
specified as a pair of numbers(e.g. a-b, [a,b])
what is measurement resolution
the smallest change in the measurement of a measuring device that can be observed
what is measurement error?
sensors can provide values that have errors
when measuring an item using tape errors an come from:
-tape elasticity
- tape shifting while measuring
-temperature of the item being measured and the tape
why are statistics needed in measurement?
measuring an item once is not enough, two values need to be presented
1. average
2. deviating from average(uncertainty)
what is gaussian distribution?
normal distribution
a bell-shaped curve, and it is assumed that during any measurement values will follow a normal distribution with an equal number of measurements above and below the mean value.
what is an outlier?
An outlier is an experimental data point not following the underlying distribution of points.
what is the sampling theorem?
a way of ensuring that an original signal can be reconstructed from a finite set of samples
what is Aliasing?
high frequency chances that appear as low frequencies
what is sampling frequency?
number of times per second a given sensor is read
(v, measured in Hz)
what is sampling period?
the time elapsed between 2 consecutive readings of one sensor
(T, measured in seconds)
what is a proprioceptive robotic sensor?
measuring an internal robot variable; battery level, motor temp, encoders…
what is a exteroceptive robot sensor
measures external (environmental) variables; distance sensors, compass, bumpers, cameras…
what is an active robot sensor?
sensors that measure the effect of something they put in the environment; laser scanners, encoders, Kinect…
what is a passive robot sensor?
measure some variable that is in the environment; compass, camera…
what is a bump sensor?
-Passive sensors that detect contact with objects
-Binary sensors, generally switches with some electronics
-Contact ON / Non-contact OFF
-They are being substituted by touch sensors (pressure,
temperature. . . ).
-Not very elegant to rely on them (last resort) Robots usually are surrounded by these sensors
what are the pros of bump sensors?
-cheap and small
-notify of crashes
what are the cons of bump sensors
-short range
-on means the robot has crashed
-not directional
what is an infra-red sensor?
an electronic device that measures and detects infrared radiation in its surrounding environment.
what are the pros of infra-red sensors?
cheap and small
directional
what are the cons of infra-red sensors?
-short-range
-read reflectance (need calibration)
-sensitive to colour
-sensitive to electronics tolerance
what is a time of flight (ToF) sensor?
an active sensor that measures the time a sent-out wave takes to fly forth and back to the sensor after hitting an object
what is an ultra-sound sensor (ToF)
-active sensors based on ultra-sound reflected from obstacles
-vibrating metal sheet & associated electronics
-emitter and detector are the same
-sound intensity decays with the distance
robots usually have rings of ultra-sound sensors
what are the pros of ultra-sound sensors?
-cheap and small
-sound speed almost constant (= 340m/s)
what are the cons of ultra sound sensors?
-low directionality and side lobes
-specular reflections
-multiple paths
-cross-talks (between sonars)
-animals are sensitive to them
what is a laser scanner?
active sensors that use laser light to detect obstacles
what are the 2 main types of laser scanners
-time of flight
-phase shift (modulated light pulses)
what are the pros of laser scanners?
-very precise with high directionality
-provides relative obstacle positions
-up to 360° angular range
-high frequency readings (16 Hz)
what are the cons of laser scanners?
-expensive
-affected by dust and fog
-problems detecting mirrors and glass
-high power consumption
