CE315-6-SP


UNIVERSITY OF ESSEX

Undergraduate Examinations 2019



MOBILE ROBOTICS



Time allowed: TWO hours


Candidates are permitted to bring into the examination room:
Calculators – Casio FX-83GT Plus or Casio FX-85GT Plus ONLY


The paper consists of FOUR questions.


Candidates must answer all FOUR questions.


Questions are NOT of equal weight.


The percentages shown in brackets provide an indication of the proportion of the total marks
for the PAPER which will be allocated.







Please do not leave your seat unless you are given permission by an invigilator.
Do not communicate in any way with any other candidate in the examination room.
Do not open the question paper until told to do so.
All answers must be written in the answer book(s) provided and not on rough paper.
All rough work must be written in the answer book(s) provided. A line should be
drawn through any rough work to indicate to the examiner that it is not part of the
work to be marked.
At the end of the examination, remain seated until your answer book(s) have been
collected and you have been told you may leave.



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Question 1


Odometry is widely used in the navigation process of mobile robots for its simplicity and real-
time performance. However, its systematic and non-systematic errors make it unreliable
during long-time operation, so error correction by other sensors is necessary.


(a) List 5 systematic errors and 3 non-systematic errors in odometry calculation.


(b) Use a flow chart to describe the odometry calculation process that can be used in a
mobile robot.


(c) The equations for odometry calculation of a differential-drive robot are


t
W
VV
kk
t
VV
kyky
t
VV
kxkx
lr
lr
lr









*)(
sin
2
)()1(
cos
2
)()1(




Assume the parameters are

Calculate the robot trajectory points (x (k), y (k)) from k=0 to k=10 using the odometry
equations above.



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Question 2


(a) In a phase measurement system, a laser transmitter generates a modulated laser signal
with a frequency of 15 MHz at a speed of 610325 m/s.

How far is the object from the sensor system when the phase-shift detector measures
that the phase delay in the return signal is 1.2 radians?


(b) Figure 2.1 shows a stereo vision system employing two CCD cameras to locate one
object, P. The focal length of two cameras is 60mm and two cameras are located
280mm apart on the robot.

When it is approaching the object, a pixel point representing the point P on the object is
20mm from the centre of left camera lens.

The corresponding right camera pixel is 18mm from the centre of its camera lens. What
is the range of the object?

Figure 2.1 A stereo vision system















[10%]
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P
Left side
of scene
Right side
of scene
Focal
length
lx
rx
Range
Distance between
two cameras
Right
camera
lensLeft
camera
lens
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Question 3


(a) Figure 3.1 shows a mobile robot that is to navigate in the environment. The robot is
equipped with two whiskers at the front, which give a binary signal when in contact
with an object, and two wheel encoders.

Explain how this robot could localise and navigate in the environment shown in
Figure 3.1.



Figure 3.1 Layout of the environment the robot is navigating in.


(b) Behaviour-based robotics enables mobile robots to navigate in an uncertain and
unpredictable world without pre-planning. In this course, you have learnt how to define
and coordinate robot behaviours and how to build behaviour-based reactive systems.
Answer the following questions:
(i) What are robot behaviours?
(ii) Describe two primary methods used for behavioural coordination.
(iii) What behaviour coordination method will you use if you have been asked to
design a vacuum cleaning robot? Justify your answer.

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Question 4


A mobile robot equipped with on-board sensors, computers and batteries has been deployed in
a golf course, as shown in Figure 4.1, to mow the grass. The robot is a car-like, and has a pair
of steering wheels at its front and a pair of driving wheels at its back. Its task is to navigate
and mow the grass twice a week, and charge the on-board batteries when the voltage is low.
There is a charging point and a grass storage place in the golf course.

Suppose that the robot is provided with an environment map, including trees and pond. There
is no information related to the moving obstacles. The criterions for implementing this task
are:

 The robot must mow the whole course without unnecessary repeating.
 The robot must not hit any obstacles (e.g. trees, people, etc.) while carrying out this task.
 The robot must empty its grass storage bag when the bag is full.
 The robot must return to the charging point when completing the task.
Figure 4.1 A golf course


Suppose that your task is to design the computer architecture for the robot to implement the
specified task using behaviour-based approach. Answer the following design questions:


(a) Define a set of robot behaviours that are needed for this application.


(b) Use the RS (Robot Schema) model to express the robot behaviours defined above.


(c) Discuss what sensors you would use in your design in order to enable the robot to
implement the specified task.



END OF PAPER CE315-6-SP
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