23-04-2011, 04:32 PM
PRESENTED BY
FARDEEN UMAR
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CRUISE CONTROL
Introduction to ACC
PRINCIPLE OF ACC
ACC works by detecting the distance and speed of the vehicles ahead by using either a Lidar system or a Radar system [1, 2].The time taken by the transmission and reception is the key of the distance measurement while the shift in frequency of the reflected beam by Doppler Effect is measured to know the speed.
CONSTITUENTS OF AN ACC SYSTEM:
A sensor (LIDAR or RADAR) usually kept behind the grill of the vehicle to obtain the information regarding the vehicle ahead. The relevant target data may be velocity, distance, angular position and lateral acceleration.
Longitudinal controller which receives the sensor data and process it to generate the commands to the actuators of brakes throttle or gear box using Control Area Network (CAN) of the vehicle.
LIDAR
PULSE DOPPLER RADAR
EFFECT OF DOPPLER SHIFT:
Thus, the waves arrive with decreasing intervals of time between them.
fD = 2·v
λ
where,
fD = Doppler Frequency [Hz] λ = wavelength [m] v = speed of the wave-source [m/s]
The phase shift is given by
φ = 2r · 2π
λ
where,
φ = phase-difference between the transmitted and the received signal 2r = the distance: the way and the way back 2π = 360°: the period of an oscillation λ = wavelength of the transmitted energy
If the aim has the radial speed
vr = d®/dt
then the value of the phase changes to
d(φ) = - 4π·vr
dt λ
This is equivalent to the Doppler- frequency fD according to:
fD = 1 · d(φ) = 1 · - 4π · vr
2π dt 2π λ
| fD| = 2 · vr= 2 · vr· ftx
λ c0
where: ftx = is the transmitters frequency c0 = is the speed of the light vr = is the radial speed of the aim λ c0
This means: In practice the Doppler- frequency occurs twice at a radar. Once on the way from the radar to the aim, and then for the reflected (and already afflicted by a Doppler-shift) energy on the way back.
FUSION SENSOR
SPACE OF MANEUVERABILITY AND STOPPING DISTANCE If the curve radius of a possible trajectory is ‘r’ for a given velocity ‘v’ and sideways acceleration ‘ay’ ,then r=v² / ay. The stopping distance is given by, Ds = .5 u² /ax + td u, where ‘u’ is the initial speed ‘td’ is the time taken by the system to receive and process the sensor data and ‘ax’ is the acceleration of the vehicle .
