A Study On Path Guidance System Of Guide Robot For Visually Impaired
Dong Fan Shen, Se Kee Kil, Tae Jin Jang, *Eung Hyuk Lee, Seung Hong Hong
Department of Electronic Engineering, Inha University
*Department of Electronic Engineering, Korea Polytechnic University
E-mail : shiner819@empal.com, kclips@hanmail.net, jang_tae_jin@hotmail.com,
*ehlee@kpu.ac.kr, shhong@inha.ac.kr
Abstract : In this paper, earth coordinate of the
guidance robot for the visually impaired is detected
by using GPS (Global Position System), and the
system which leads the visually impaired to position
information (TM coordinate) in Korea is achieved
through map-matching with electronic map. The
visually impaired need more information about the
walking path than ordinary people when walking
outdoor. Therefore, we studied implementation
which can guide the visually impaired more safely
through map-matching with GPS signal by making
electronic map for the visually impaired.
Keywords: Guide Robot, GPS, Map-matching,
According to the research on the handicapped
person in 2000, the number of the visually
impaired in Korea is assumed by 180,000
persons where is more than double in number
than 70,000 persons of 1995. While, welfare
facilities for the visually impaired are still in a
primitive level as at most Braille type block on
side-walk or signal lamp's walk guide by sound.
The outside activities of the visually impaired
are heavily depending upon the use of white
canes or guide dogs. However white cane is not
an ensuring mean of safety and guide dog is not
cost effective, not in wide use. Assistant
equipment for the visually impaired has been on
demand to address the problems and guides them
Recently, RTA(Robotic Travel Aids) system
using mobile robot is widely studied as a guide
system for the visually impaired. HARUNOBU of
the Yamanashi University in Japan is the
representative example.
In this paper, the implementation that the
guidance robot for the visually impaired guides the
visually impaired in safety is studied in this paper.
Because the guidance robot for the visually
impaired should guide to the destination in safety, the
path of the guidance robot could be different from
that of the ordinary people. Therefore, the electronic
maps concerned about the characteristic of the
visually impaired are necessary.
In this paper, the walking path and destination are
determined by making the electronic map for the
visually impaired including directions, distance, and
types of the walking path which are necessary when
the visually impaired are walking outdoor. Also, the
system that the location of the guidance robot is
presumed by using GPS signal and then the guidance
robot guides the visually impaired in safety through
map-matching between the electronic map and GPS
signals is implemented.
The system based on the PDA especially enabled
the visually impaired to walk alone carrying with the
PDA and the GPS receiver without the guidance
Figure 1 shows the system conception of the
visually impaired walk with the guidance robot
wearing bone-conduction headphone and carrying
with PDA. The bone-conduction headphone is the
thing that provides necessary information to the
visually impaired as sound, and PDA matches GPS
signal from the robot by radio communication to the
map. In order to input the destination where the
visually impaired want to go, the braille keypad is
attached on the screen of PDA.
Figure 2 shows the block diagram of the guidance
system. In generally, the digital map is focus to
car navigation system and difficult to apply to
blind man guidance. Therefor, we composed the
guidance system with two part, guardian system
and user system. First system is made a new
map layer for blind man, next is guidance
system using the map layer.
crosswalk, and the overpass etc. Therefore, the
proper way to detour according to kind of path for
safety must be selected in case of deciding the
optimal path.
The type of path in the link are the sidewalk with
the braille block and without the braille block, the
road that cars and people pass together, the
crosswalk, the stairs, and the overpass. The safer
path is selected among each same distant paths using
different weights as dangerous levels.
Figure 3 shows the electronic map for the visually
impaired around Inha University. Solid lines and
dotted lines that are shown in figure 2 are paths, the
"link", that the visually impaired can walk, and ◎
indications are the "node" that indicates the
destination that the visually impaired can select. The
family of the visually impaired can update the
electronic map as the visually impaired want because
the links and the nodes in the electronic map could be
modified in the softwares based on PC.
Figure 1. System Conception
2. path for blind
Figure 2. Syste block diagram
2.1 Guardian Part program base on PC
The electronic map for the visually impaired
includes the information which is necessary while
walking. The 1:1000 electronic map has layers which
consist of information for the visually impaired.
Compared to the general electronic map, the link that
has the directions, distance, and types of the walking
path for the visually impaired and the node that
points out the destination which the visually impaired
can select are added.
The visually impaired are difficult to walk in the
sidewalk without the braille block, the road, the
1. Flow chart
3. the layer for blind
Figure 3. Guardian program
2.2 User Part program based on PDA
Figure 4 show the diagram of the user program
in PDA.
Figure 4. The diagram of PDA system
Initialization is include device initialize and
create a undirected weighted graph for searching
the path. we presented the graph with
adjacency-list method. Each vertex in the graph
have maximum four edge and define six weight
values for distinct path kind.
GPS receiver part processing NMEA string
parsing and coordinate convert from WGS84 to
TM in korea using Molodensky-Badekas model.
In the NMEA0813 sentences, we used GPRMC
sentence for position information, use PDOP, and
SNR from GPGSV sentence for estimate the
error of GPS.
The user interface is composed braille keypad
input system and voice output system using tts
engine. hence, user can select the destination
name with ARS method. In addition we made
braille keypad using PDA touch screen.
The guide algorithm have path detection
algorithm and map matching algorithm. While
the optimal path for the ordinary people is the
shortest path, that for the visually impaired
should be concerned about safety first of all. In
this paper, the method which decides the optimal
path for safety of the visually impaired is
proposed using Back Tracking algorithm. Also,
the graph for the determination of path combines
the necessary information for the visually
impaired's walking. Back Tracking algorithm is
DFS (Depth-First Search). DFS is that any
search algorithm which considers outgoing edges
of a vertex before any neighbors of the vertex,
that is, outgoing edges of the vertex's
predecessor in the search. Extremes are searched
first. This is easily implemented with recursion.
An algorithm which marks all vertexes in a
directed graph in the order they are discovered
and finished, partitioning the graph into a forest.
If the value exceeds the determined limit in the
Back Tracking algorithm, then it comes back to
the vertex which was selected in the previous
step. In the process of searching the optimal
path using Back Tracking algorithm, the path
detours in case of danger. Furthermore, if the
visually impaired want to minimize the number
of overpasses and crosswalks, not the shortest
path but the optimal path could be selected
through the adjustment of the number of
specified type.
The modified point-to-curve matching method is
point-to-curve matching method is the method
that projects to the nearest arc after measuring
the distance from each received points. Because
this method has the advantage of easy and fast
operation due to little amount of measuring, it is
more efficient than other algorithms in the
map-matching method. However, this method
could mismatches to the wrong road around two
roads near the crosswalk due to the error of
GPS. In this paper, the way of a 1st order
equation that minimizes error in the data
including error is used by the information of
robot's moving direction. In addition, the method
that the error is revised at the next received
point is added to improve map-matching using
error between received and matched point.
For this experiment, RGM2000 GPS reception
module of Royaltec company is attached on
IPAQ H3850 PDA using RS232C. The produced
information of electronic map is stored in PDA
through PDA cradle. PDA receives GPS
information by NMEA way through RS232c, and
map-matches to the received map information, then
composes guidance information through drawing the
location in Korea, and guides as sound through
TTS(Text-To-Speech) engine.
Figure 5 shows GPS receiver and PDA that
composes for an experiment.
Figure 5. The experiment system
(left is input screen, right is guide screen)
In order to recognize how much GPS reception
signal and actuality walk path show difference, the
GPS signals were received around actual residental
walking paths. GPS data that received through PDA
simulated in PC.
Figure 6 indicates is targeted real path for
experiment. And GPS signals that were received by
actual walking around residental area in the Inha
university. Figure 7 show the received GPS data.
Figure 8 shows the map matching result.
The result shows that except for area A, B, C,
other path's data show good results almost same
as actual walking.
Figure 8. Map matching result
The area of A, B is a alley, and area C has a
high-rise building. Therefor, there are serious
multi-path error. The table 1 shows the
mismatching error(Nmber of mismatching data /
total Number of received data) in two different
environment. The table describe the environment
with PDOP value. With PDOP lower than 6, can
get good matching result. In the case of cycle
slip and PDOP>10, the GPS data is have too
much error to use it. Therefor, the high PDOP
value means the bad environment for receiving
GPS signal.
Table 1. Influence of the environment
Num of data
Cycle slip error
Matching error
Figure 6. Real Path
Experiment 1 Experiment 2
Even if, with lower PDOP GPS data, also have
big absolute error. Figure 9 shows the error and
PDOP in a rectilinear movement.
Figure 7. GPS Data
Figure 9. Error and PDOP in Rectilinear
In the area A GPS data have lower PDOP value, but
the error is more than 10m and become higher.
Therefor the rate of PDOP is also a important factor
to estimate GPS error.
In connection with the implementation of
guidance robot for the visually impaired,
map-matching between GPS and electronic map
which is for self localization and determination
of right path of robot is studied in this paper.
map-matching received GPS signal to the
optimal path in the electronic map, although it is
similar with real walking path, a few miss
map-matching cases occurred at the difficult
points to receive.
In case of big error, that is, map-matching is
failed, if map-matching is achieved not only
depending on the GPS signal but also with INS
of robot, the result may be more correct.
Furthermore, although the starting point of the
guidance robot cannot be known exactly using
GPS reception signal, it is helpful to implement
if the starting point is detected through the
vision sensor and so on.
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