Lecture 3: Perception_Sensors Flashcards
In AI, what’s easy and what’s hard?
The hard problems are easy and the easy problems are hard.
What is the definition of perception?
Places/situations→Objects→Features→Raw Data
Raw Data→Features→Objects→Places/situations
Name all the common sensors and their use in mobile robotics
Tactile sensors or bumpers: detection of physical contact, security switches
GPS: global localization and navigation
Inertial Measurement Unit(IMU): Orientation and acceleration of the robot
Wheel Encoders: Local motion estimation(odometry)
Laser Scanners: Obstacle avoidance, motion estimation, scene interpretation
Cameras: Texture information, motion estimation, scene interpretation
What is an encoder?
a communication device that controls the motion of an operating device
How do encoders provide help?
(det 4 things; s,p,d,c)
help determine the speed, position, direction, or counts of a motor or other moving equipment
Name the four encoder technologies.
Magnetic, mechanical, resistive, optical
What is a linear encoder?
(linear search into a/d signal)
a sensor traducer with a scale that encodes position into analog or digital signal
What is a rotary encoder?
(em dev..conv angu pos to a/d code)
an electromechanical device with a scaled disk that converts the angular position or motion to an analog or digital code
What can Incremental Encoders do and not do?
(both deal with the same thing)
They can measure the change in position, but not specify the position relative to a known reference
What happens to incremental encoders every time the device is switched on or reset?
it begins counting from 0 and it generates an output signal each time the shaft moves.
What does an Absolute encoder do?
It provides the digital output, which represents the absolute displacement.
What happens when an Absolute Encoder system is switched on?
It immediately measure the value of the actual position.
What about the disc of an Absolute Encoder?
It uses a Gray code in which one-bit changes at a time, which reduces encoder communication errors.
What is the operational principle of the ultrasonic Range sensor?
an ultrasonic pulse is generated by a piezo-electric emitter, reflected by an object in its path, and sensed by a piezo-electric receiver; based on the speed of sound in air and the elapsed time from emission to reception, the distance between the sensor and the object is easily calculated.
What are the main characteristics of the Ultrasonic Range Sensor?
(prec infl .. ang)
-the precision influenced by angle to object
-useful in ranges from several centimeters to several meters
-typically, relatively inexpensive
What are the 2 applications of the Ultrasonic Range Sensor?
(Dm, Cd)
Distance Measurement and Collision Detection
What are the 4 limitations of Ultrasonic Range Sensor?
(not dir, soft sur, per sur, low up)
It is not directive; it’s like an opening cone.
There are soft surfaces that absorb most of the sound energy.
There are surfaces that are fare from being perpendicular to the direction of the sound, specular reflections.
There is a low update frequency(speed of sound)
What do the GPS satellites send?
Their orbital location, aka as ephemeris, plus time
How does the receiver of the GPS satellite compute its location?
trilateration and time correction.
What is the working principle of the Global Positioning System?
the location is determined through a time-of-flight measurement between the satellites and user.
What are the 4 technical challenges of the GPS?
(Time Synce, Real time, Precise Measurement, Interference)
Time synchronization between individual satellites and the GPS receiver
Real time update of the exact location of the satellites
Precise measurement of the time-of-flight
Interferences with other signals
What can be said about Time Synchronization?
(Ultra-preci, atomic, ground)
Ultra-precision time synchronization is very important.
There are atomic clocks on each satellite.
Monitoring them from different ground stations.
How fast does electromagnetic radiation travel?
roughly 0.3 meter per nanosecond
What is the relation between position accuracy and the precision of time measurement?
Position accuracy is proportional to the precision of time measurement
What does a master station do for the real-time update of the exact location of the satellites?
It analyzes all the measurements and transmits the actual position to each of the satellites
What about the exact measurement of the time of flight?
(Quartz, range)
Quartz clock on the GPS receivers are not very precise
The range measurement with four satellites allows to identify the three values (x, y, z) for the position and the clock correction ∆𝑇
What is the nominal position accuracy of commercial GPS receivers?
around 3 meters
What are the 2 ways the local environment interfere with the GPS?
Through:
Signal Obstruction-physical structures prevent GPS satellite signals from reaching the receiver
Multipath Error-Radio waves have traveled paths of different lengths between the transmitter(the satellite) and the receiver
What is the Inertial Measurement Unit?
(…est rel pos,v,ac)
It is a device that uses gyroscopes and accelerometers to estimate the relative position, velocity, and acceleration of a moving vehicle.
What is another way of calling the IMU? What does it have?
(iNs)
Inertial Navigation System, and it has a common navigational component of aircraft and ships.
What does the INS/IMU estimate?
(6 letters)
It estimates the six-degree-of-freedom(DOF) pose of the vehicle: position(x,y,z) and orientation(roll, pitch, yaw)
What can be said about gyroscopes?
(h..ing sensors …orient)
It has heading sensors that preserve their orientation in relation to a fixed reference frame.
What can be said about mechanical gyroscopes?
(Think of IMU and (m)otor)
It relies on the inertial properties of a fast-spinning rotor
What can be said about optical gyroscopes?
(Think eyes, things you can see)
It has angular speed sensors that use two monochromatic light beams,, or lasers, emitted from the same source
What can be said about accelerometers?
(s-m-d sys)
It is a a spring-mass-damper system used to measure all external forces acting upon it, including gravity.
