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E359 L9 - Coggle Diagram

- - - - lane change or imminent crash detection and mitigation, a shorter range but wider field of view is desired
      - advanced cruise control or crash avoidance, a longer range but narrower field of view is required
  - - - Cheap
      - Work normally in low visibility and low light conditions
    - - Can only be used at low speeds, for example during parking
      - Shorter field of view and accuracy compared to LiDAR
  - - - Heavily used in automated vehicle research, and deployed in some safety applications
    - - Low-cost, off-the-shelf components
      - Implementation is almost entirely in software
    - - Implemented as passive sensors, thus must cope with full range of ambient and uncontrolled conditions, including lighting,
      - shadowing and reflection, and atmospheric weather, dust, and smoke
      - Requires a lot of processing power from the controller, which also increases heat generation
- - - - example include Global Positioning System (GPS) to determine geographic location
  - - - example include Camera to perceive road markings, LiDAR to detect obstacles
  - - - Example include Hall effect sensor to measure vehicle velocity, Inertial Measurement Unit (IMU) to measure acceleration
  - - - The error between the true value and its measurement, which may include noise levels and external interference rejection parameters
    - - The minimum difference between two measurements (often much lesser than the actual accuracy of the sensor)
    - - The smallest value that can be detected or measured
    - - The minimum and maximum values that can be (accurately) detected
    - - Quantities such as sensor range or its field of view (FOV)
    - - Quantities such as update rate of sensor output and the frequency bandwidth of the measurement output over time
    - - How the information is transmitted from the sensor to controller (eg. Analogue voltage or current, digital outputs, serial or network data streams)
- - - - Measures linear acceleration
      - example
        
        Piezoelectric accelerometer
        
        Piezoelectric material is sandwiched between 2 masses or plates and the force acting on masses compress or expand the piezoelectric material, generating an electrical potential
        
        Microelectro-mechanical systems (MEMS) accelerometer
        
        A beam deflects in response to accelerations, which changes the capacitance between itself and a fixed beam
    - - Measures rotational rate
      - example
        
        MEMS gyroscope
        
        Tuning fork structure: 2 proof masses oscillate in opposition resonance and out of plane motion is measured
        
        Piezoelectric structure: Angular rotation induces an out of plane motion through Coriolis forces
        
        Wine glass resonator: Nodal positions indicate rotational rates
        
        Ring laser gyroscope and Fibre optic gyroscope
        
        2 light beams travel in opposite directions around a closed path
        
        Angular rotations induce a difference in path length, causing a phase shift, and interference fringe patterns can be measured by a Sagnac interferometer
    - - Measures direction, strength or relative charge of a magnetic field
        In IMUs, vector magnetometers are used to measure the direction of magnetic field to determine the vehicle’s heading (absolute yaw angle)
      - example
        
        Fluxgate magnetometer
        
        Oscillating voltage is fed into primary coil of a transformer
        
        The presence of external magnetic field along the axis of the transformer will cause a difference in the current in the secondary coil, which is used to estimate the strength of the external magnetic field
        
        Hall effect magnetometer
        
        The presence of external magnetic field perpendicular to direction of current flow in the sensor will produce an electric potential on the sensing element
        
        Magnetoresistive magnetometer
        
        Presence of external magnetic field will change the electrical resistance of the magnetoresistive alloy
        
        The change in resistance is detected when it causes a voltage imbalance in a Whetstone bridge
    - - Racelogic IMU RLVBIMU04
- - - - Absolute position
      - Velocity and orientation
      - Precise time and synchronised pulse per second
      - Raw information that can be used for precise post-processing applications