Robot navigation in unknown environment with obstacle recognition using laser sensor

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 9, No. 3, June 2019, pp. 1773∼1779
ISSN: 2088-8708, DOI: 10.11591/ijece.v9i3.pp1773-1779 Ì 1773
Robot navigation in unknown environment with obstacle
recognition using laser sensor
Neerendra Kumar1
, Zoltán Vámossy2
1,2
John von Neumann Faculty of Informatics, Óbuda University, Hungary
1
Department of Computer Science & IT, Central University of Jammu, India
Article Info
Article history:
Received Jun 5, 2018
Revised Nov 19, 2018
Accepted Des 15, 2018
Keywords:
Laser scan
Obstacle avoidance
Obstacle recognition
Robot navigation
Turtlebot
ABSTRACT
Robot navigation in unknown and dynamic environments may result in aimless wan-
dering, corner traps and repetitive path loops. To address these issues, this paper
presents the solution by comparing the standard deviation of the distance ranges of the
obstacles appeared in the robot navigation path. For the similar obstacles, The standard
deviations of distance range vectors, obtained from the laser range finder sensor of the
robot at similar pose, are very close to each other. Therefore, the measurements of
odometer sensor are also combined with the standard deviation to recognize the loca-
tion of the obstacles. A novel algorithm, with obstacle detection feature, is presented
for robot navigation in unknown and dynamic environments. The algorithm checks
the similarity of the distance range vectors of the obstacles in the path and uses this
information in combination with the odometer measurements to identify the obstacles
and their locations. The experimental work is carried out using Gazebo simulator.
Copyright c 2019 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Neerendra Kumar,
John von Neumann Faculty of Informatics, Óbuda University,
Bécsi út 96/b, H-1034 Budapest, Hungary.
Email: neerendra.kumar@phd.uni-obuda.hu
1. INTRODUCTION
Autonomous navigation of robots is gaining popularity among the researchers day by day. Regardless
of the uncertainties in the sensors observations, robot may navigate safely from start to goal [1]. Using range
finder sensors (e.g. laser scan sensors), the robot can navigate from start to goal with obstacle avoidance in
unknown and dynamic environments environment [2]. The obstacle size and velocity vector of the unmanned
surface vehicles can be used to achieve the obstacle avoidance. Moreover, fusion of more than one navigation
algorithms can result more accurate outcomes [3]. Various requirements of obstacle avoidance can be satisfied
for the changing distance between robot and the obstacles [4]. The issue of obstacle avoidance is treated as
an optimization problem in [5]. On the unmarked path, dynamic colour perception model for the autonomous
navigation is explained in [6]. Nevertheless, this model is not suitable for the laser range finder sensors. The
complexity of the object matching task rises for similar objects [7]. Previous experiences during the robot
navigation are helpful to predict the path with obstacle avoidance of static and dynamic obstacles [8]. Tool
based learning for robots is presented by [9]. In case of industrial robots, an algorithm for condition monitoring
using artificial intelligence is studied in [10]. An algorithm for obstacles avoidance in unknown environment
using bumper events of the robot is proposed in [11]. However, the algorithm presented in [11] has the limitation
that the robot may struck in the corners and may follow the same loop of the path again and again. A fuzzy
controller for obstacle avoidance in unknown environment is presented in [12]. Although, the fuzzy rules, for
the obstacles in the central part of the laser scan area, are right or left biased. Therefore, the robot may trap in a
repetitive navigation path loop in some situations. In this paper, the scan range vectors are compared to detect
the previously occurred obstacles on the same locations of the navigation path.
Journal homepage: http://iaescore.com/journals/index.php/IJECE

1774 Ì ISSN: 2088-8708
2. PROBLEM DEFINITION AND PROPOSED ALGORITHM
During robot navigation in unknown environment, the robot may trap in a loop and may repeat the
same path again and again. This may be due to the presence of static or dynamic obstacles. To deal with this
type of problem, there is a need to ﬁnd a method which can recognize the previously occurred obstacles in
successive repetition of the path. So that, the robot can be directed to reverse the angular velocity applied so
far. In this way, the robot will come out of the repetitive navigation path loop.
Algorithm 1 Obstacle recognition using laser sensor and odometer
1: Create vectors: U, V, X, Y, T, S;
2: Initialize: Rmax, g, Dt, c, Ts, Tf , σt, Pt, vc, ωc, vb;
3: while (Time < Tf ) do
4: R ← scan ranges received;
5: for i ← 1 to length of R do
6: if R(i) == NaN then
7: R(i) ← Rmax;
8: end if
9: end for
10: g ← g + 1;
11: Collect odometer readings at the time of scan;
X(g) ← X coordinate from odometer;
Y(g) ← Y coordinate from odometer;
12: Dmin ← minimum of R;
13: if Dmin < Dt then
14: c ← c + 1;
15: σ ← standard deviation of R;
16: S(c) ← σ;
17: U(c) ← X coordinate from odometer;
18: V(c) ← Y coordinate from odometer;
19: T(c) ← time of scan;
20: for j ← 1 to (length of S − 1) do
21: Dj,c ← (U(c) − U(j))2 + (V(c) − V(j))2 ;
22: σr ← |(S(c) − S(j))|;
23: if (σr < σt and Dj,c < Pt) then
24: Match found between scans j and c.
Record corresponding scan times and positions of robot with respect to j and
c.;
25: end if
26: end for
27: v ← −|vb|;
28: ω ← ωc;
29: else
30: v ← vc;
31: ω ← 0;
32: end if
33: Send v, ω to robot;
34: end while
The laser scanning is a reliable method for obstacles range ﬁnding. Generally, the laser scanner
produces a vector of ranges (R) of obstacles. If there are n number of readings in a scan then R can be
expressed by (1) as follows:
R = [dk], for k = 1 to n. (1)
Where, d is a distance range.
Int J Elec & Comp Eng, Vol. 9, No. 3, June 2019 : 1773 – 1779

Int J Elec & Comp Eng ISSN: 2088-8708 Ì 1775
Standard deviation (σ) of R can be expressed by (2) as given below:
σ =
n
k (dk − d)2
n
. (2)
Where, d is the mean of R.
Standard deviations of two range vectors can be compared to ﬁnd the similarity between them. If
the standard deviations of the two scan range vectors are close enough then there is the possibility that these
scans belongs to the same obstacle. Further, the standard deviation in combination of the robot position coor-
dinates can be used to conﬁrm that the scan ranges belongs to the same obstacle. To achieve this solution, the
Algorithm 1 is presented.
3. EXPERIMENTAL RESULTS AND DISCUSSION
The proposed Algorithm 1 is implemented using a notebook computer equipped with 4xIntel Core
i3 CPU @ 230 GHz. The memory of the system is 3952MB. Ubuntu 14.04.5 LTS operating system is used.
Robotics System Toolbox The memory of the system is 3952MB. Ubuntu 14.04.5 LTS operating system is used.
Robotics System Toolbox in MATLAB (R2018a) is applied for computer programs. Simulated Turtlebot robot
model is taken in Gazebo 2.2.6 simulator. The numerical values of the variables, initialized in Algorithm 1, are
presented in Table 1.
Table 1. Description of variables and initialized values
Variable Description Initialized Value
Rmax Maximum range of the laser scanner Default
g a counter variable 0
Dt Threshold distance of robot and obstacles 0.6 (meter)
c a counter variable 0
Ts Starting time 0
Tf Finish time 80 (seconds)
σt Threshold difference between σ of two scans 0.0005
Pt Threshold distance between two positions 0.2 (meter)
vc Forward linear velocity 0.5 (meter/sec.)
ωc Angular velocity −0.6 (radian/sec.)
vb Backward linear velocity −0.02 (meter/sec.)
v Published linear velocity -
ω Published angular velocity -
U X coordinates of poses when obstacles are near -
V Y coordinates of poses when obstacles are near -
X X coordinates of all poses -
Y Y coordinates of all poses -
T Time at scans performed -
S
Standard deviations
scan range vectors
-
The robot is driven, using Algorithm 1, in the Gazebo world as given by Figure 1. In the beginning,
in Figure 1, the Turtlebot is located at the centre of the world and heading towards positive X axis. In Figure 1,
coordinate axes and their measurement marker are added to provide the understanding of the coordinate po-
sitions in the Gazebo world. The Gazebo world is constructed by using brick boxes of the dimensions 3x1x3
from the model database of the Gazebo simulator. Purposely, The Gazebo world is constructed using only one
model so that the same type of obstacle encountered each time to increase the complexity in differentiating the
obstacles and their respective locations. In addition, the maze structure is kept closed so that the robot can be
forced to follow a repeated path in a loop. The Gazebo world and the simulated Turtlebot can be brought up in
the system by executing the following command in a terminal of Ubuntu:
Robot navigation in unknown environment with obstacle recognition using laser sensor (Neerendra Kumar)

1776 Ì ISSN: 2088-8708
roslaunch turtlebot_gazebo turtlebot_world.launch world_file:=file name
-3 -2 -1 0 1 2 3
X (meters)
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
Y(meters)
Figure 1. Simulated world in Gazebo.
Robot is driven at a constant forward linear velocity and zero angular velocity until any closed obstacle
is encountered. In this navigation process, if any obstacle is closed enough to the robot then a backward linear
velocity and a constant non zero angular velocity is provided to the robot. Using Algorithm 1, the robot
navigates in a path loop. Figure 2 shows the resultant path of the robot. It is clear from Figure 2 that robot is
driven in a navigation loop so that it can observe the same obstacles more than once. During the navigation
process, the obstacles distances are measured by laser scan ranges. For Turtlebot, a laser scan message contains
a vector of 640 range readings of the scan area from right to left. If robot pose is same, each time, the laser scan
of an obstacle produces same vector of ranges. To find the similarity between two vectors of ranges, standard
deviations of the two vectors are compared.
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
X (meters)
-1.5
-1
-0.5
0
0.5
1
1.5
Y(meters)
Robot navigation path
Robot positions
Figure 2. Robot path generated from odometer measurements.
Figure 3 presents the standard deviations of the range vectors of different scans performed during the
navigation of the robot. Figure 3 depicts that there are periodic spikes which are due to the similarity of the
obstacles and repetitive path loop. Further, the pattern of the graph in the periods is found very similar to each
other because of the similarity of the obstacles. Subsequently, it can be inferred that the standard deviations
of the similar obstacles are observed close to each other. However, in addition to the standard deviation, the
odometer measurements, for the robot locations during the navigation, are used to determine the location of the
obstacles. Further, on the basis of the standard deviations and odometer measurements, it can not be identified
that either the obstacle was visited by the robot previously or the obstacle is encountered first time during the
navigation. For this reason, there is the need for additional method to recognize that whether any particular
obstacle is found first time or it is repeated. The occurrence number (i.e. first time encountered or repeated) of

an obstacle can be described on the basis of the time of the scan. Obviously, the standard deviations and robot
positions of two nearby scans at very short time of difference will not vary largely. On the other hand, if the
standard deviations of the distance range vectors of any two scans and the robot positions received from the
odometer at the time of scans are very close to each for both of the scans and the time difference between the
two scans is large than a threshold value then it can be said that the obstacle is same and the occurrence of this
obstacle is the repeated one.
0 50 100 150 200
Scan number
1.7
1.75
1.8
1.85
1.9
1.95
2
2.05
Standarddeviation(meters)
Standard deviation of scans
Figure 3. Standard deviation of scan ranges.
Table 2 presents the positions of the robot and their corresponding times with respect to scan range
matches. It can be observed from the Table 2 that using standard deviations and robot positions the similarity
between the two scan range vectors are found either at times with short difference or at times where the time
interval is larger. The matches at short and large time intervals indicates about the occurrence time of the
obstacles. For example, the ﬁrst row of Table 2 indicates that the match between the range vectors is found at
the scan times 10.23 (seconds) and 10.46 (seconds). Thus, the time interval (Time2 − Time1) between these
scans is less than a second. Keeping in mind the forward linear velocity of the robot (i.e. 0.5 meter/seconds),
it is clear that the scans were performed at nearly same time therefore the match is found between the ﬁrst
appearance of the obstacle and this is not the case of repetition. Similarly, the last row of the Table 2 presents
the time interval between the scans as 34.57 (seconds). Therefore, on the basis of robot’s linear and angular
velocities it can be deduced that the occurrence of the obstacle at Time2 (at last row) is repeated in navigation
path loop.
Table 2. Laser scan range vectors matches and robot positions
Time1 (Sec.) Time2 (Sec.) Scan Numbers Matched Robot Position at Time1 Robot Position at Time2
10.23 10.46 35, 37 (1.59, -1.11) (1.59, -1.11)
19.08 21.28 48, 63 (-1.66, -0.99) (-1.67, -0.93)
21.73 21.84 64, 65 (-1.69, -0.86) (-1.70, -0.81)
26.32 26.44 69, 70 (-1.64, 1.05) (-1.64, 1.05)
28.68 28.8 85, 86 (-1.60, 1.05) (-1.55, 1.06)
37.62 38.64 95, 103 (1.59, 1.01) (1.57, 1.02)
37.17 39.66 92, 107 (1.59, 1.01) (1.61, 0.89)
9.68 44.91 31, 113 (1.59, -1.12) (1.51, -1.07)
9.68 45.13 31, 115 (1.59, -1.12) (1.51, -1.08)
10.56 45.13 38, 115 (1.60, -1.11) (1.51, -1.08)

1778 Ì ISSN: 2088-8708
4. CONCLUSION
Using the standard deviation of laser scan range vectors, the similarity of obstacles is examined in
unknown environment. In addition to the standard deviation, the robot position is also used to identify whether
the obstacle position is same as of some earlier position during the navigation path loop. It is evident from the
Table 2 that the matches between scan range vectors are found at the closed positions of the robot in each round
of the navigation loop. Time interval between the scans plays an important role in the detection of the repetitive
occurrences of the obstacles. Using the standard deviation of laser scan range vectors, robot positions and time
of scan, the angular velocity can be reversed to break the path loop.
ACKNOWLEDGEMENT
This study is inspired by the TekiControl research project of John von Neumann Faculty of Informatics,
Óbuda University, Budapest, Hungary.
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BIOGRAPHY OF AUTHORS
Neerendra Kumar is Assistant Professor at Department of Computer Science and IT, Central
University of Jammu, India. His teaching interest are in Artiﬁcial intelligence, Programming
languages, Algorithm analysis and Robotics. He has received Stipendium Hungaricum Schol-
arship award in 2015 for the duration of three years. He is doing his PhD studies at John von
Neumann Faculty of Informatics, Óbuda University, Budapest, Hungary. His research area is
robot navigation. His Scopus and ORCID IDs are 57190585849 and 0000-0002-6609-8974,
respectively.
The detailed information can be accessed on the following URL:
http://cujammu.ac.in//5084/5084_media/nareendra.pdf
Zoltán Vámossy is Associate Professor at John von Neumann Faculty of Informatics, Óbuda
University, Budapest, Hungary. He has completed his PhD from Budapest University of
Technology and Economics, Hungary in 2010. The area of his PhD studies include Navigating
mobile robots with machine vision based on PAL optics. His current research interests are
focused on mobile robotics, robot navigation, image processing and computer vision. He
has received various awards including the János Neumann Award (János Neumann Computer
Science Association) in 2016.
For Further information please visit the URL: http://uni-obuda.hu/en/node/701

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