Lecture 3: Perception_Sensors

Question 1

In AI, what’s easy and what’s hard?

Answer 1

The hard problems are easy and the easy problems are hard.

Question 2

What is the definition of perception?

Answer 2

Places/situations→Objects→Features→Raw Data
Raw Data→Features→Objects→Places/situations

Question 3

Name all the common sensors and their use in mobile robotics

Answer 3

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

Question 4

What is an encoder?

Answer 4

a communication device that controls the motion of an operating device

Question 5

How do encoders provide help?
(det 4 things; s,p,d,c)

Answer 5

help determine the speed, position, direction, or counts of a motor or other moving equipment

Question 6

Name the four encoder technologies.

Answer 6

Magnetic, mechanical, resistive, optical

Question 7

What is a linear encoder?
(linear search into a/d signal)

Answer 7

a sensor traducer with a scale that encodes position into analog or digital signal

Question 8

What is a rotary encoder?
(em dev..conv angu pos to a/d code)

Answer 8

an electromechanical device with a scaled disk that converts the angular position or motion to an analog or digital code

Question 9

What can Incremental Encoders do and not do?
(both deal with the same thing)

Answer 9

They can measure the change in position, but not specify the position relative to a known reference

Question 10

What happens to incremental encoders every time the device is switched on or reset?

Answer 10

it begins counting from 0 and it generates an output signal each time the shaft moves.

Question 11

What does an Absolute encoder do?

Answer 11

It provides the digital output, which represents the absolute displacement.

Question 12

What happens when an Absolute Encoder system is switched on?

Answer 12

It immediately measure the value of the actual position.

Question 13

What about the disc of an Absolute Encoder?

Answer 13

It uses a Gray code in which one-bit changes at a time, which reduces encoder communication errors.

Question 14

What is the operational principle of the ultrasonic Range sensor?

Answer 14

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.

Question 15

What are the main characteristics of the Ultrasonic Range Sensor?
(prec infl .. ang)

Answer 15

-the precision influenced by angle to object
-useful in ranges from several centimeters to several meters
-typically, relatively inexpensive

Question 16

What are the 2 applications of the Ultrasonic Range Sensor?
(Dm, Cd)

Answer 16

Distance Measurement and Collision Detection

Question 17

What are the 4 limitations of Ultrasonic Range Sensor?
(not dir, soft sur, per sur, low up)

Answer 17

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)

Question 18

What do the GPS satellites send?

Answer 18

Their orbital location, aka as ephemeris, plus time

Question 19

How does the receiver of the GPS satellite compute its location?

Answer 19

trilateration and time correction.

Question 20

What is the working principle of the Global Positioning System?

Answer 20

the location is determined through a time-of-flight measurement between the satellites and user.

Question 21

What are the 4 technical challenges of the GPS?
(Time Synce, Real time, Precise Measurement, Interference)

Answer 21

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

Question 22

What can be said about Time Synchronization?
(Ultra-preci, atomic, ground)

Answer 22

Ultra-precision time synchronization is very important.
There are atomic clocks on each satellite.
Monitoring them from different ground stations.

Question 23

How fast does electromagnetic radiation travel?

Answer 23

roughly 0.3 meter per nanosecond

Question 24

What is the relation between position accuracy and the precision of time measurement?

Answer 24

Position accuracy is proportional to the precision of time measurement

Question 25

What does a master station do for the real-time update of the exact location of the satellites?

Answer 25

It analyzes all the measurements and transmits the actual position to each of the satellites

Question 26

What about the exact measurement of the time of flight?
(Quartz, range)

Answer 26

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

Question 27

What is the nominal position accuracy of commercial GPS receivers?

Answer 27

around 3 meters

Question 28

What are the 2 ways the local environment interfere with the GPS?

Answer 28

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

Question 29

What is the Inertial Measurement Unit?
(…est rel pos,v,ac)

Answer 29

It is a device that uses gyroscopes and accelerometers to estimate the relative position, velocity, and acceleration of a moving vehicle.

Question 30

What is another way of calling the IMU? What does it have?
(iNs)

Answer 30

Inertial Navigation System, and it has a common navigational component of aircraft and ships.

Question 31

What does the INS/IMU estimate?
(6 letters)

Answer 31

It estimates the six-degree-of-freedom(DOF) pose of the vehicle: position(x,y,z) and orientation(roll, pitch, yaw)

Question 32

What can be said about gyroscopes?
(h..ing sensors …orient)

Answer 32

It has heading sensors that preserve their orientation in relation to a fixed reference frame.

Question 33

What can be said about mechanical gyroscopes?
(Think of IMU and (m)otor)

Answer 33

It relies on the inertial properties of a fast-spinning rotor

Question 34

What can be said about optical gyroscopes?
(Think eyes, things you can see)

Answer 34

It has angular speed sensors that use two monochromatic light beams,, or lasers, emitted from the same source

Question 35

What can be said about accelerometers?
(s-m-d sys)

Answer 35

It is a a spring-mass-damper system used to measure all external forces acting upon it, including gravity.