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Active Vehicle And Traffic Safety > Sensors > Flashcards

Sensors Flashcards

1
Q

What is a sensor?

A

“A device which is used to record that something is present or that there are changes in something”

  • “Digitally” acquire data from sensors
  • Subjective data (such as data acquired from questionnaires)
  • (Map data)
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2
Q

What is an actuator?

A
  • “a servomechanism that supplies and transmits a measured amount of energy for the operation of another mechanism or system.”
  • “a mechanical device for moving or controlling something“

Servomechanism: a powered mechanism producing motion or forces at a higher level of energy than the input level, e.g. in the brakes and steering of large motor vehicles, especially where feedback is employed to make the control automatic.

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3
Q

Difference between Accuracy and Precision?

A

Accuracy is how close a measured value is to the actual (true) value.

Precision is how close the measured values are to each other.

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4
Q

What is ADAS short for?

A

ADAS – advanced driver assistance system. A term subsuming active safety.

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5
Q

What does OEM stands for?

A

OEM – original equipment manufacturer. Typically vehicle manufacturer

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6
Q

What does Tier 1 supplier mean?

A

Tier 1 supplier – a supplier that supplied directly to the OEMs

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7
Q

What is RADAR short for?

A

RADAR – Radio Detection and Ranging

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8
Q

LIDAR is short for?

A

LIDAR – Light Detection And Ranging.

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9
Q

CAN is short for?

A

CAN - Controller Area Network. In vehicle electronic bus system

Controller Area Network, CAN eller CAN-buss, är en databuss främst avsedd för fordon, men som numera även används i andra sammanhang. CAN möjliggör att flera noder eller styrenheter i fordonet kan sända meddelanden till varandra på ett säkert och snabbt sätt.

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10
Q

Active Safety Sensors - Examples for Vehicle Control.

A

Vehicle control

  • Braking (e.g. pressure)
  • Acc. Pedal (e.g. linear motion)
  • Steering wheel (e.g. angle)
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11
Q

Active Safety Sensors - Example Kinematics:

A

Kinematics

  • Acceleration (e.g. lateral)
  • Angle rate (e.g. yaw rate)
  • Angle (e.g. pitch or roll)
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12
Q

Active Safety Sensors - Longitudinal external examples:

A

Longitudinal external

  • Range/ range rate / object angle (e.g. RADAR, LIDAR, GPS, vision (camera), sonar)
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13
Q

Active Safety Sensors - Lateral external examples

A

Lateral external

  • Lateral position (LIDAR, vision, GPS+map)
  • Angle rate (e.g. yaw rate)
  • Angle (e.g. pitch or roll)
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14
Q

Active Safety Sensors - Other examples

A

Other

  • Map data
  • Eye/head tracker
  • Night vision
  • Time-of-flight cameras
  • In-vehicle button handling
  • Etc…
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15
Q

Explain Vehicle-control sensors Pressure

A

Pressure

  • Measures e.g. brake pressure [unit: e.g. bar]
  • Brake pressure:
    • Driver pressurize with foot
    • Brake system “primes” brakes for faster response
    • ADAS can control brakes (preferably primed)
  • Careful when interpreting
    • “who/what did what”?
  • E.g. for:
    • Closed-loop control of braking in ADAS
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16
Q

Explain Vehicle - control sensors Angular/rotary position

A

Angular/rotary position

  • Measures rotation [e.g. degrees, radians or revolutions] {Resolution: ~0.5deg – 0.01deg}
  • Used for steering wheel, wheels etc.
  • Several approaches
    • Encoder based
    • Resistance based (potentiometers)
    • Magnetic
    • Hall effect sensors
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17
Q

Explain Vehicle - control sensors Linear position

A

Linear position

  • Measures linear position [mm]
  • Easy to use and interpret
  • Transformation of linear motion to rotation common
    • Example: ”draw wire”
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18
Q

Vehicle kinematics sensors - Accelerometers

A

Accelerometers

  • Measures acceleration [m/s 2 or g (gravity ~10m/s 2)]
  • Often 3-axis (x/y/z). X most often forward in automotive applications.
  • Rotation can be misinterpreted (centripetal)
  • Range and frequency depend on application
  • E.g. for:
    • Closed-loop control in ADAS
    • Complementary in sensor fusion
    • Can be used as “angle sensor” with gravity (motion a problem)
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19
Q

Vehicle kinematics sensors - What to consider when working with accelerometers

A

Accelerometers

When working with accelerometers:

  • Make sure that the range is appropriate for your measurement task (e.g., not -+40g when you measure vehicle dynamics)
  • Make sure your least-significant-bit is appropriate
  • They do not like being dropped on hard surfaces…
  • Consider offsets – if possible calibrate on “zero deceleration” times
  • Integrated acceleration is speed, but needs an “initial condition”. Also very likely the integrated speed “drifts” due to acceleration offset.
20
Q

Vehicle kinematics sensors - Angular rate

A

Angular rate

  • Measures how fast something rotates [radians / second]
  • 1-3 axis sensors
  • Integration gives angle, but integration sensitive to drift!
  • Micro mechanical, piezo-electrical etc
  • E.g. for:
    • Closed-loop control in ADAS (stability control)
    • Complementary in sensor fusion dead reckoning (e.g. when GPS loss)
21
Q

What happens when we integrate acceleration or angular rate?

A

Angle

  • Measures absolute angle (e.g. pitch or roll) [deg or rad]
  • Acceleration problematic – rotation affects value
  • Integration of angular rate problematic – integration errors
  • Sensors:
    • Earth magnetic field possible –needs continuous calibration
    • Accelerometer
    • Angular rate (gyros)
  • E.g. for:
    • Sensor “calibration”
    • In passive safety
22
Q

”Longitudinal” sensors implies

A

…Range, range rate and angle to other objects

23
Q

Different Longitudinal Sensors

A

Different sensors

  • RADAR – Radio Detection and Ranging
  • LIDAR – Light Detection and Ranging
  • Vision – Different types of camera based sensor solutions
  • GPS - Global Positioning System
24
Q

Compare Radar, Lidar, Vision based on:

  • Range
  • Angle
  • Velocity
  • Night Capability
  • All-weather Capability
  • Object Classification
A
25
Q

Explain RADAR

A
26
Q

What is the RADAR performance?

A

RADAR performance

  • Normal distances: up to150-200m
  • Distance depends on radar cross section (truck >car>motorcycle) • Issue with loosing track of targets and re-acquiring
  • Separation of objects e.g. 3 degrees
27
Q

What is the LIDAR principle?

A
28
Q

Explain Static Lidar.

A
29
Q

Explain Moving Lidar.

A
30
Q

How does LIDAR data looks?

A
31
Q

Differences between LIDAR and RADAR

A

LIDAR and RADAR differences

  • LIDAR often has moving parts
  • LIDAR often better angular resolution
  • LIDAR so far more expensive (scanning)
  • Velocity by Doppler effect in RADAR (not possible with LIDAR)
  • LIDAR has more weather issues
32
Q

Explain briefly the Doppler effect:

A

The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave for an observer who is moving relative to the wave source.[1] It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.

A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession

33
Q

Vision systems: Camera based sensing Applications

A

Camera based applications

  • Detection and tracking of other vehicles
    • e.g. range and range rate
  • Lateral positioning (e.g. lane position)
  • Pedestrian detection and tracking
  • Sign recognition
34
Q

Explain CMOS and CDC

A
35
Q

Differences between Frame-transfer and Interlace in Camera based applications

A

Frame-transfer vs Interlace

  • How the image is captured
  • Frame-transfer: The whole image “at ones”
  • Interlaced: Every other row at ~50/60Hz (PAL/NTSC)
36
Q

Issues with Interlacing?

A
37
Q

Frame-transfer vs rolling shutter Camera Based Vision

A

Frame-transfer vs rolling shutter

  • How the image is captured
    • Frame-transfer: The whole image “at ones”
    • Rolling shutter: reading out line-by-line
      • the first line will be an earlier capture of the scene than the last
38
Q

How to lane/road position

A

Lane/road position

  • Vision (tracking road markings etc)
  • LIDAR (different reflectivity – aimed downwards)
39
Q

What is different with night vision cameras?

A
40
Q

What does Time-Of-Flight Cameras measure?

A
41
Q

What is eye tracking?

A

A measurement (tracking) of the direction of the drivers gaze (“the direction the eyes are pointing”) in relation to some coordinate system.

42
Q

Explain Visual Distraction Detection.

A
43
Q

In-vehicle systems on the market and in the future (Eye+Head tracking)

A

In-vehicle systems on the market and in the future

  • Current:
    • ”Eyes-on-road” (eyes-on-road) -> attention allocation
  • Future (examples):
    • Visual attention in traffic environment context
    • Identification of driver actions
44
Q

Explain In-Vehicle button handling.

A

In-Vehicle button handling

What is the driver doing in the car?

  • Many sensors in the vehicle available on CAN:
    • What buttons has the driver pushed, and when?
    • Temperature, distance traveled, seat position, driver ID?
45
Q

What do you think takes the most time when performing research (as well as when performing studies in industry)?

A
46
Q
A

Active Vehicle And Traffic Safety (7 decks)

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