29-05-2012, 11:29 AM
Automatic Cruise Control System
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Abstract
The thesis introduces a novel approach for longitudinal motion control of vehicles. Different
traffic densities are found to demand different behavior from vehicles to optimize the
usage of roadways. Infact, studies have shown that the use of automatic cruise control structure
in congested traffic often result in excessive braking and accelerations. Also the use of
automatic cruise control system in city roadways is prohibited as per the state and federal
laws. We propose a methodology in which automatic cruise control structure is used at
high speed situations where the traffic density is low to moderate, and a reference modelbased
control structure is used during stop-and-go traffic situations, common in many city
roadways especially during peak hours. The former control structure objective is to followthe-
leader car, while the latter control structure ensures that a car is stopped before critical
distance is reached while respecting the comfort specifications during stop-and-go scenario.
The reference model used is non-linear and provides dynamic solutions consistent with safety
constraints and comfort specifications. Each of the above controllers is used as a master
controller of the cascade control scheme. A common slave controller is used for the two
cascade control schemes. The slave (inner) feedback loop is used to compensate unmodeled
dynamics and external disturbances (for e.g. road slopes). The experiments performed on
Dexter-6C and (relatively low-cost) CDBOT vehicular robots, shows that the use of cascade
control structure produces equally good performances from the two vehicular robots.
Acknowledgment
I thank my guide Prof. Kannan Moudgalya, for his continuous support in my M.Tech.
program. He showed me different ways to approach a research problem. He was always there
when I need his support and technical help. He is responsible for all the goals I achieved in
my entire M.Tech. program. I also thank my co-guide Prof. Krithi Ramamritham, who gave
me this project work and gave me an opportunity to work in ERTS laboratory, KReSIT, IIT
Bombay.
A special thanks goes to Prof Kian-Lee, Tan, who guided me during second stage of
the project work at School of Computing (SoC), National University of Singapore (NUS).
Without his encouragements and constant guidance, I could not have finished second stage
work. He was always there to meet and talk about my ideas and proofread my papers, articles,
and to ask me good questions to help me think through my problems (weather philosophical,
analytical or computational) Also thanks to folks at Database Research Laboratory, SoC,
NUS especially, Amit, my partner for daily lunch and snacks at Singapore.
Besides my supervisors, I would like to thank colleagues at ERTS laboratory, a wonderful
workplace and my home for almost a year (which included first and third stage of the project
work). Let me also say ‘thank you’ to the following people at ERTS laboratory: Sachitanand
Malewar, Ashish Gudhe, Guru, and Amey. I will remember for a long time the ‘evening
snacks’ we used to have at ‘Upahar’ near Y-gate of IIT Bombay.
I am also greatly indebted to my teachers in the past: P. Gawande, Punwatkar, B. Yadav,
R. Patil, and M/s Alice Lazar, who introduced me to the field of controls and encouraged
me to pursue my interests.
I thank my ‘guru’s’, Anand Zambare and Mishra Sir, for guiding me at various stages of
my life, for encouraging me to pursue my interests, even the interests went beyond boundaries
of language, field, and geography. I am greatly indebted to them for unconditional support
and encouragement.
I am also thankful to my close friends: Vishal, Vijay, Sarvesh, and Adhish for their moral
support, for listening to my complaints and frustrations, for believing in me and for spending
memorable time with me.
Last but not the least, I thank my family: my parents, Shri Sonu Budho Kakade, and
Shrimati Kamal Sonu Kakade, for giving me life in the first place, for educating me, for
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unconditional support and encouragement to pursue my interests. My elder brother Nitin,
for sharing his experiences with me and for supporting me in difficult times; and my younger
brother Arun, for sweet time we spend together, and for his caring nature towards me.
Finally I am thankful to my father for reminding me that my research work should always
be useful and serve good purposes to all humankind.
Introduction
As automation technology has progressed, especially in the decades after the invention of the
integrated circuit, more and more functions have been added to automobiles, relieving the
driver of much of the mundane moment-to-moment decision making that may be regarded as
having made driving tedious. Several groups which include researchers from several universities,
research laboratories, automotive industry, transport authorities, technology providers,
research organizations, insurance industry, road operators etc. are working on intelligent or
smart car development programs. Such programs work for adding more and more functions
to automobiles. Examples of smart car features are:
1. Computerized engine management systems
2. Anti-lock Braking Systems (ABS)
3. Position monitoring system or lane departure warning system
4. Platoon and car-train features
5. Automatic Cruise Control (ACC) system
6. Advanced Parking Guidance (APG) system
7. Collision warning system
This project studies automatic cruise control (ACC) system in detail. ACC is an automated
modification to the cruise control (sometimes known to as speed control or Autocruise)
systems. In cruise control system driver sets the speed and system takes over the control
of throttle of the car to maintain the same speed. Cruise control system is expected to
maintain the same speed whether up hill or down. Cruise controls currently being developed
include the ability to automatically reduce speed when the speed limit decreases. This is
an advantage for those driving in unfamiliar areas. Cruise controls often prove useful for
long drives across sparsely populated roads. This usually results in better fuel efficiency.
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Cruise control systems are disengaged automatically, when driver hits the brake or clutch.
However, such disengagement may also result in driver loosing control of the car. This is true
especially during inclement weather or while driving on wet or snow covered roads. Cruise
control system often proves less useful on moderate traffic, where driver has to disengage the
cruise control system whenever he/she finds closing in vehicle in front. This fact led to a
development of system referred to as Automatic Cruise Control (ACC) system. Following
section describes ACC system in detail.
1.1 Automatic cruise control (ACC)
Automatic cruise control (ACC) refers to a smart car with some automatic functionality
including a routine task of cruise control on highways. As mentioned earlier ACC system
has the ability to detect the presence of vehicle in front. This is done with the use of either
laser or radar range finder which allow vehicle to keep pace with the the car it is following,
slow when closing in on the vehicle in front and accelerating again to the preset speed when
traffic allows. Overall objective of the system is to adjust the speed of the car to maintain
a safe following distance. A forward looking range finder detects the speed and distance of
the vehicle in front.
Automatic cruise control is similar to conventional cruise control in that it maintains
the vehicle’s preset speed. However, unlike conventional cruise control, this new system
can automatically adjust speed in order to maintain a safe distance between vehicles in the
same lane. It proves to be more useful than cruise control system in low and moderate
traffic situations. However dense traffic may result in stop-and-go behavior from vehicles
trapped in traffic congestion. Traffic congestion typically occurs when traffic demand is
greater than the capacity of a road (or of the intersections along the road). In general,
stop-and-go behavior leads to a considerable wastage of fuel, increased air pollution due
to increased idling, acceleration, and braking, increased journey times thus wasting time of
motorist and passengers, and increasing the frustration of motorists. Blocked traffic may also
interfere with the passage of emergency vehicles traveling to their destinations where they
are urgently needed. Dense traffic therefore demands a different behavior from vehicles so as
to minimize if not to eliminate negative impacts the traffic congestion may have. Following
section details about the stop-and-go behavior of traffic.
In this project work we have attempted to design the control system for automatic cruise
control to be used in low and moderate traffic situations, and a separate control system to
be used in congested traffic situations. More about this is given in section 1.3 and following
chapters.
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0 0.2 0.4 0.6 0.8 1
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
k/kj
q/ckj
Figure 1.1: Fundamental flow diagram.
1.2 Stop-and-go traffic Situation
From above discussion it is clear that a cruise control is useful only for sparsely populated
roads. For most of the traffic volumes or regions in fundamental traffic diagram shown
in Fig. 1.1, automatic cruise control is necessary to avoid driver continuously disengaging
system like cruise control. However, according state federal laws the use of ACC system
at low velocities is prohibited. Thus, forcing human driving in stop-and-go traffic where
usually average speed of the cars is below 10 km/hr. It is found that the human driving in
(frustrating) stop-and-go scenario generally, results in excessive decelerations and jerks, thus
violating the comfort specifications. Therefore, it is the high traffic density region which
demands a different behavior of cars to avoid prolonged congestion and increased journey
times. Typically, we agree upon-
1. One can control traffic behind by slowing down, but he/she cannot control traffic ahead
by speeding up.
2. One can control the traffic jam before he/she gets trapped inside it. In other words, one
must behave differently before the jam, and not while he/she is trapped inside it.
3. Traffic jam is a phenomenon where from the outflow has become constant, which means
driver of a car in the jam can’t affect outflow of the jam. On the other hand, in noncongested
traffic the traffic outflow is a function of inflow.
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4. By eliminating a space ahead, one becomes a part of an impenetrable wall which creates
a dynamic bottleneck.
The conclusion is to have a different control strategy from ACC which mainly aims at car
following or inter-distance control. This new control strategy which is active in stop-and-go
traffic has the safety and comfort as the main goals. The car is expected not to alleviate the
comfort constraints such as maximum deceleration and maximum jerk while at the same time
safety constraint must also be obeyed. It is the objective of this report to study automatic
cruise control and the control in stop-and-go traffic together to ensure a safe inter-distance
following in low and moderate traffic volume situations, and a safe and comfortable ride in
high traffic volume situations. In this regard we present a novel cascade control scheme to
control the longitudinal motion of the vehicle.
1.3 Objectives of the project
As mentioned, the objective of this project is to have a automotive cruise control system that
performs a safe inter-distance control and also reacts differently when the traffic volume is
high enough to produce stop-and-go traffic behavior. Speed of the cars is used as the index
to separate traffic congestion from non-congested traffic. This is a valid assumption as it will
be shown later that the speed of traffic stream generally decreases as the density rises. Thus
below a certain speed value, for example 10 km/hr, the traffic stream is expected to exhibit
a stop-and-go kind of behavior. The control law designed for ACC in the first stage of the
project is used for car-following, while a reference model-based control approach is used to
obtain the control law for congested traffic.
These two control laws are combined with the feedback control loop to form a cascade
control structure, where ACC or reference model based controller forms the master controller
and the inner feedback controller forms the slave controller. The inner feedback control loop
is designed to reject the influence of unmodeled dynamics and external disturbances such as
road slopes.
Experiments are performed on the robotic vehicle platform, CDBOT, to asses the control
system performances. The target platform is a low cost vehicular robot built at Embedded
Real Time Systems (ERTS) laboratory, KReSIT, IIT Bombay. The results of experiments
are satisfactory and suggest the benefits of the control structure described in this report.
Another objective of the project was to implement the control strategies on such a low cost
platform, which was accomplished.
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1.4 Organization of the report
Chapter 1 gave the introduction and objectives of the project. In chapter 2, literature on the
relevant fields such as traffic flow theory, automatic cruise control system and control of cars
in congested traffic are reviewed. Shortcomings of already available methods are discussed
along with the specific aspects on longitudinal control of cars in stop-and-go traffic, those
remained unexplored in literature are discussed in chapter 2. In addition to this, chapter
2 also presents the literature review on the selection of sampling period for such a timecritical
applications, and the safe spacing policy which takes in to account the follower vehicle
parameters such as maximum velocity, acceleration/deceleration, and jerk to compute the
safe inter-distance. Chapter 3 gives the detailed mathematical formulation and analysis of
control law designed for ACC and longitudinal control in congested traffic. Chapter 4 includes
the brief overview on the implementation of cascade control structure and also discusses the
experimental results. Finally, chapter 5 includes the concluding remarks on this project work.
Suggested future improvements are given in chapter 6.