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Seminar ’03 NavBelt and GuideCane
INTRODUCTION
Recent revolutionary achievements in robotics and bioengineering have
given scientists and engineers great opportunities and challenges to serve
humanity. This seminar is about “NAVBELT AND GUIDECANE”, which are two
computerised devices based on advanced mobile robotic navigation for obstacle
avoidance useful for visually impaired people. This is “Bioengineering for
people with disabilities”.
NavBelt is worn by the user like a belt and is equipped with an array of
ultrasonic sensors. It provides acoustic signals via a set of stereo earphones that
guide the user around obstacles or displace a virtual acoustic panoramic image of
the traveller’s surroundings. One limitation of the NavBelt is that it is
exceedingly difficult for the user to comprehend the guidance signals in time, to
allow fast work.
A newer device, called GuideCane, effectively overcomes this problem.
The GuideCane uses the same mobile robotics technology as the NavBelt but is a
wheeled device pushed ahead of the user via an attached cane. When the Guide
Cane detects an obstacle, it steers around it. The user immediately feels this
steering action and can follow the Guide Cane’s new path easily without any
conscious effort. The mechanical, electrical and software components, user-
machine interface and the prototypes of the two devices are described below.
Dept. of AEI MESCE, Kuttippuram1
Seminar ’03 NavBelt and GuideCane
MOBILE ROBOTICS TECHNOLOGIES FOR THE
VISUALLY IMPAIRED.
With the development of radar and ultrasonic technologies over the past
four decades, a new series of devices, known as Electronic Travel Aids (ETA’s),
was developed. This seminar introduces two novel ETA’s that differ from the
ETA’s like C5 laser cane, Mowat sensor, in their ability to not only detect
obstacles but also to guide the user around detected obstacles.
Obstacle Avoidance Systems (OAS) originally developed for mobile
robots, lend themselves well to incorporation in Electronic Travel Aids for the
visually impaired. An OAS for mobile robots typically comprises a set of,
ultrasonic or other sensors and the computer algorithm that uses the sensor data
to compute the safe path around detected obstacle. One such algorithm is the
Vector Field Histogram (VFH).
The VFH method is based on information perceived by an array of
ultrasonic sensors (also called Sonars) and a fast statistical analysis of that
information. The VFH method builds and continuously upgrades a local map of
its immediate surroundings based on recent Sonar data history. The algorithm
then computes a momentary steering direction and travel speed and sends this
information to the mobile robot. The ultrasonic sensors are controlled by the
Error-Eliminating Rapid Ultrasonic Firing (EERUF) method. This method
allows Sonars to fire at rates that are five to ten times faster than conventional
methods.
Dept. of AEI MESCE, Kuttippuram2
Seminar ’03 NavBelt and GuideCane
FIGURE 1
Dept. of AEI MESCE, Kuttippuram3
Seminar ’03 NavBelt and GuideCane
In the VHF method, the local map is represented by a two-dimensional
(2D) array, called a Histogram Grid. The 2D Histogram Grid is reduced to a
one-dimensional Polar Histogram that is constructed around the robot’s
momentary location. The Polar Histogram provides an instantaneous 360˚
panoramic view of the immediate environment, in which elevations suggests the
presence of obstacles, and valleys suggests that the corresponding directions are
free of obstacles. The Polar Histogram has 72 sectors that are each 5˚ wide. The
numeric values associated with each sector are called Obstacle Density Values.
Figure (1), shows the Polar Histogram created from an actual experiment,
wherein, high Obstacle Density Values are shown as taller bars in the bar chart-
type representation. Hence, the Polar Histogram provides comprehensive
information about the environment (with regard to obstacles).
N AV B ELT
The NavBelt consists of a belt, a portable computer, and an array of
ultrasonic sensors mounted on the front of the belt. Eight ultrasonic sensors, each
covering a sector of 15˚ are mounted on the front pack, providing a total scan
range of 120˚.The computer processes the signals that arrive from the sensors and
applies the robotic obstacle-avoidance algorithms. The acoustic signals are
relayed to the user by stereophonic headphones. Figure (2), shows the
experimental prototype of the device and pictorial representation of it’s concept.
Dept. of AEI MESCE, Kuttippuram4
Seminar ’03 NavBelt and GuideCane
FIGURE 2
Dept. of AEI MESCE, Kuttippuram5
Seminar ’03 NavBelt and GuideCane
A binaural feedback system based on internal time difference (i.e. the
phase difference between the left and right ears) and amplitude difference (i.e.
the difference in amplitude between the two ears) creates a virtual direction (i.e.
an impression of directionality of virtual sound sources). The binaural feedback
system is used differently in each of the three operational modes.
OPERATIONAL MODES: - The NavBelt is designed for three basic
operational modes, each offering a different type of assistance to the user.
Guidance Mode: -
In the guidance mode, the NavBelt only provides the user with the
recommended travel speed and direction, generated by the VFH obstacle-
avoidance algorithm. In this mode, the system attempts to bring the user to a
specified absolute target location. The VFH (Vector Field Histogram) method
calculates its recommendation for the momentary travel direction from the polar
histogram by searching for sectors with a low obstacle density value. Next, the
VFH algorithm searches for the candidate sector that is nearest to the direction of
the target and recommends it to the user. The recommended travel speed is
determined by the VFH method according to the proximity of the user to the
nearest object. The recommended travel speed and direction are relayed to the
user by a single stereophonic signal. An important parameter involved in the
guidance mode is the rate at which signals are transmitted. When the user is
travelling in an unfamiliar environment cluttered with a large number of
Dept. of AEI MESCE, Kuttippuram6
Seminar ’03 NavBelt and GuideCane
obstacles, the transmission rate increases and may reach up to 10 signals per
second. On the other hand, when travelling in an environment with little or no
obstacles, the transmission rate is one signal every three second.
Directional-Guidance Mode: -
In this mode, the traveller uses a joystick or other suitable input devices to
define a temporary target direction as follows – when the joystick is in its neutral
position, the system selects a default direction straight ahead of the user no
matter which may the user is facing. If the user wishes to turn sideways, he/she
deflects the joystick in the desired direction, and a momentary target is selected
5-mt. diagonally ahead of the user in that direction. In case an obstacle is
detected, the NavBelt provides the user with relevant information to avoid the
obstacle with minimal deviation from the target direction. The recommended
travel speed and direction are conveyed to the user through a single stereophonic
signal, similar to the method used in the guidance mode. This mode gives the
user more control over the global aspects of the navigation task.
Image Mode: -
This mode presents the user with a panoramic virtual acoustic image of
the environment. A virtual acoustic image is a stereophonic sound that appears to
travel through the user’s head from the right to the left ear. A virtual beam travels
from the right side of the user to the left through the sectors covered by the
NavBelt’s sonar’s (a range of 120˚ and 3-mt radius). The binaural feedback
Dept. of AEI MESCE, Kuttippuram7
Seminar ’03 NavBelt and GuideCane
system invokes the impression of a virtual sound source moving with the beam
from the right to the left ear in what we call a “sweep”. This is done in several
discrete steps, corresponding to the discrete virtual direction steps. Figure (3)
shows the graphical representation of the image mode.
Dept. of AEI MESCE, Kuttippuram8
Seminar ’03 NavBelt and GuideCane
At each step, the amplitude of the signal is set proportionally to the
distance of the obstacle in that virtual direction. If no obstacles are in a given
virtual direction, the virtual sound source is of a low amplitude and barely
audible. Otherwise, the amplitude of the virtual sound source is larger. One of the
important feature of the image mode is the Acoustic Directional Intensity (ADI),
which is directly derived from the polar histogram. The virtual direction of the
ADI provides information about the source of the auditory signal in space,
indicating the location of an object. The intensity of the signals is proportional to
the size of the object and its distance from the person as derived from the polar
histogram. The ADI is a combination of the signal duration Ts, the amplitude A,
and the pitch.
Dept. of AEI MESCE, Kuttippuram9
Seminar ’03 NavBelt and GuideCane
ADVANTAGES
NavBelt can detect objects as narrow as 10mm.
NavBelt can reliably detect objects with a diameter of 10cm or
more, regardless of the travel speed.
The current detection range of the NavBelt is set for 3mt.
DISADVANTAGES
For object with diameter of 10mm, the detection is possible if the
objects are stationary or the subject is walking slowly (less than 0.4 m/s).
NavBelt lacked the ability to detect overhanging objects, steps,
sidewalks, edges etc. This can be removed by addition of Sonars pointing
up and down to detect these types of obstacles.
It does not allow fast-motion.
The NavBelt uses a 2-D representation of the environment. The
representation of this type becomes unsafe when travelling near
overhanging object or approaching bumps and holes.
The above disadvantage can be removed by substantial modifications to
the obstacle-avoidance algorithm and to the auditory interface.
IMPROVEMENTS
The Nav Belt is currently not able to detect over hanging objects. This
problem can be removed by using a camera and a laser scanner attached to a
special helmet, which can detect objects according to the user’s head orientation.
Adding more sonars to the front pack of the Nav Belt (pointing upwards and
downwards) can provide additional information.
Dept. of AEI MESCE, Kuttippuram10
Seminar ’03 NavBelt and GuideCane
GUIDE CANE
It can be thought of as a robotic guide dog. The functional components of
the GUIDE CANE are shown in the figure. A servomotor, operating under the
control of the built-in computer, can steer the wheels left and right relative to the
cane. Both wheels are equipped with encoders to determine their relative
position. For obstacle detection, the GuideCane is equipped with ten ultrasonic
sensors, and to specify a desired direction of motion, the user operates a mini
joystick located at the handle. Based on the user input and the sensor data from
its sonar’s and encoders, the computer decides where to head next and turns the
wheels accordingly.
FUNCTIONAL DESCRIPTION
During operation, the user pushes the GuideCane forward with the help of
a thumb-operated joystick located near the handle. If the user presses the button
forward, the system considers the current direction of travel to be the desired
direction. If the user presses the button to the left, the computer adds 90˚ to the
current direction of travel and as soon as this direction is free of obstacles, steers
the wheels to the left until the 90˚ left turn is completed. Functional components
are shown in figure (4).
Dept. of AEI MESCE, Kuttippuram11
Seminar ’03 NavBelt and GuideCane
FIGURE 4
Dept. of AEI MESCE, Kuttippuram12
Seminar ’03 NavBelt and GuideCane
While travelling, the ultrasonic sensors detect any obstacles in a 120˚ wide
sector ahead of the user. The built-in computer uses the sensor data to
instantaneously determine an appropriate direction of travel. If an obstacle
blocks, the desired direction of travel the Obstacle Avoidance Algorithm
prescribes an alternative direction to circumnavigate the obstacle and then
resume in the desired direction.
Once the wheels begin to steer sideways to avoid the obstacles, the user
can feel the resulting horizontal rotation of the cane; hence, the traveller changes
his/her orientation to align himself/herself with the cane at the “nominal” angle.
Once the obstacle is cleared, the wheels steer back to the original desired
direction of travel, although the new line of travel will be offset from the original
line of travel. The Guide Cane offers separate solutions for downward and
upward steps. Downward steps are detected in a fail-safe manner:- when a
downward step is encountered, the wheels of the Guide Cane drop off the edge
until the shock-absorbing bottom hits the step – without a doubt, a signal that the
user cannot miss. Because the user walks behind the Guide Cane, he/she has
sufficient time to stop. Additional front-facing sonars can detect upward steps.
The Guide Cane analyses the environment first and then computes the
momentary optimal direction of travel. The bandwidth of information is much
smaller and hence easier and safer to follow. Figure (4) also shows the way
GuideCane avoids the obstacles.
Dept. of AEI MESCE, Kuttippuram13
Seminar ’03 NavBelt and GuideCane
HARDWARE IMPLEMENTATION
Two basic types of hardware used are: -
a) Mechanical hardware, and,
b) Electronic hardware.
a) Mechanical hardware: -
The Guide Cane must be as compact and lightweight as possible so that
user can easily lift it, e.g., for coping with steps, and for access to public
transportation. For the same reason, the electronic components should require
minimal power in order to minimize the weight of the batteries. The current
prototype uses 12AA rechargeable NiMH batteries that power the system for
two hours. The estimate of the total weight of a commercially made Guide
Cane would be approximately 2.5 kg. Figure (5) shows the mechanical
hardware of the GuideCane.
It consists of a housing, a wheelbase and a handle. The housing contains
and protects most of the electronic components as shown in the figure. The
current prototype is equipped with ten Polaroid ultrasonic sensors that are
located around the housing. Eight of the sonars are located in the front in a
semicircular fashion with an angular spacing of 15˚, thereby covering a 120˚
Dept. of AEI MESCE, Kuttippuram14
Seminar ’03 NavBelt and GuideCane
sector ahead of the Guide Cane. The other two sonars face directly sideways
and are particularly useful for following walls and going through narrow
openings, such as doorways. The wheelbase is steered by a small servomotor
and supports two unpowered wheels. Two lightweight quadrature encoders
mounted to the wheels provide data for odometry. Because the wheels are
unpowered, there is much less risk of wheel slippage. The handle serves as the
main physical interface between the user and the Guide Cane. The vertical
angle of the handle can be adjusted to accommodate user’s of different height.
At the level of the user’s hand, a joystick-like pointing device is fixed to the
handle. The pointer consists of a mouse button that the user can press with
his/her thumb in any direction.
b) Electronic hardware: -
The electronic system architecture of the Guide Cane is shown in the
figure. The main brain of the Guide Cane is an embedded PC/104 computer,
equipped with a 486 microprocessor clocked at 33MHz. The PC/104 stack
consists of four layers. Three of the modules are commercially available,
including the motherboard, the Video Graphics Array (VGA) utility module,
and a miniature 125-MB hard disk. Figure(5) also shows the electronic
hardware.
Dept. of AEI MESCE, Kuttippuram15
Seminar ’03 NavBelt and GuideCane
FIGURE 5
Dept. of AEI MESCE, Kuttippuram16
Seminar ’03 NavBelt and GuideCane
The fourth module, which is custom built, serves as the main interface
between the PC and the sensors (encoders, sonars, and potentiometers) and
actuators (main servo and brakes). The main interface executes many time
critical tasks, such as firing the sonars at specific times, constantly checking the
sonars for an echo, generating Pulse Width Modulation (PWM) signals for the
servo’s, and decoding the encoder data. The fourth module, which performs all
these tasks, is called the Microcontroller Interface Board (MCIB). The main
interface is connected to the PC’s bi-directional parallel port. The interface pre-
processes most of the sensor data before the data is read by the PC. In addition,
all communications are buffered. The pre-processing and buffering not only
minimize the communications between the PC and the interface, but also
minimize the computational burden on the PC to control the sensors and
actuators. The interface consists mainly of three MC68HC11E2 micro
controllers, two quadrature decoders, a FIFO buffer and a decoder.
MC68HC11: -
MC68HC11 is a powerful 8-bit data, 16-bit address micro controller from
Motorola with an instruction set. The MC68HC11 has in-built
EEPROM/OTPROM, RAM, digital I/O, timers, A/D converter, PWM generator
and synchronous and asynchronous communications channels. Typical current
draw is less than 10mA. Figure (6) shows the connections of MC68HC11.
Dept. of AEI MESCE, Kuttippuram17
Seminar ’03 NavBelt and GuideCane
FIGURE 6
Dept. of AEI MESCE, Kuttippuram18
Seminar ’03 NavBelt and GuideCane
ARCHITECTURE
The MC68HC11is optimised for low power consumption and high-
performance operation at but frequencies up to 4 MHz. The CPU has two 8-bit
accumulators (A&B) that cab be concatenated to provide a 16-bit double
accumulator (D). Two 16-bit index registers are present (X&Y) to provide
indexing to anywhere in the memory map. Although an 8-bit processor, the
68HC11 is a very good processor and some 16-bit instructions (add, subtract,
16*16 divide, 8*8 multiply, shift and rotate). A 16-bit stack pointer is also
present, and instructions are provided for stack manipulation. Typically
multiplexed address and data bus.
Other features include: -
Powerful bit-manipulation instructions.
Five powerful addressing modes (Immediate, Extended, Indexed,
Inherent and Relative).
Power saving STOP and WAIT modes.
Memory-mapped I/O and special functions.
Dept. of AEI MESCE, Kuttippuram19
Seminar ’03 NavBelt and GuideCane
Serial Communications Interface (SCI): -
The SCI features a full duplex Universal Asynchronous
Receiver/Transmitter system, using the non-return-to-zero (NRZ) format for
Microcontroller-to-PC connections, or to form a serial communications network
connecting several widely distributed micro controllers.
Serial Peripheral Interface (SPI): -
The SPI is capable of inter-processor communication in a- multi master
system. The SPI also enables synchronous communication between the
Microcontroller and peripheral, devices such as: -
Shift registers.
Liquid Crystal Display (LCD) drivers.
Analog to Digital Converters.
Other microprocessors.
Pulse Width Modulation: -
The MC68HC11 Family offers a selection of Pulse Width Modulation
(PWM) options to support a variety of applications. Up to six PWM, channels
can be selected to create continuous waveforms with programmable rates and
software selectable duty cycles from 0 to 100%.
Dept. of AEI MESCE, Kuttippuram20
Seminar ’03 NavBelt and GuideCane
Memory: -
The MC68HC11 Family leads in Microcontroller memory technology. In
many applications, the MC68HC11 provides a single chip solution with mask
programmed ROM or user-programmable EPROM. The MC68HC11 Family’s
RAM uses a fully static design and the contents can be preserved during periods
of processor inactivity. A 4-channel Direct Memory Access (DMA) unit on some
devices permits fast data transfer between two blocks of memory, between
registers or between registers and memory.
Timer: -
The industry standard MC68HC11 timer provides flexibility, performance
and the ease of use. The system is based on a free-running 16-bit counter with a
programmable prescalar, overflow interrupt, and separate function interrupts. It
includes additional features like, Input Captures, Output Compares, Real-Time
Interrupt, Pulse Accumulator, and Watchdog Function.
A/D Converter: -
A/D systems are available with 8 to 12 channels and 8 and 10-bit
resolution. The A/D is software programmable to provide single or continuous
conversion modes.
Dept. of AEI MESCE, Kuttippuram21
Seminar ’03 NavBelt and GuideCane
FIGURE 7
Dept. of AEI MESCE, Kuttippuram22
Seminar ’03 NavBelt and GuideCane
The embedded PC/104 computer provides a convenient development
environment. Rechargeable NiMH batteries power the entire system and thus
Guide Cane is fully autonomous in terms of power and computational resources.
The VGA module is very useful for visual verification and debugging, it is no
longer needed after development. In addition, the hard-disk module can be
eliminated in the final product because the final software can be stored in an
EPROM on the motherboard. For module tests, the PC is connected to a smaller
keyboard and a colour LCD screen that is attached to the handle below the
developer’s hand. Figure 7 shows the GuideCane prototype which was
extensively tested at the University of Michigan’s Mobile Robotics Laboratory.
Dept. of AEI MESCE, Kuttippuram23
Seminar ’03 NavBelt and GuideCane
ADVANTAGES
It allows fast walking, up to 1m/s while completing complex
manoeuvres through cluttered environments.
It can be used to travel or detect staircases.
Easy to handle, and no extensive training needed.
It rolls on wheels that are in contact with the ground, thus
allowing position estimation by odometry.
DISADVANTAGES
It uses ultrasonic sensor-based obstacle avoidance system,
which is not sufficiently reliable at detecting all obstacles under
all conditions.
It cannot detect overhanging objects like tabletops.
IMPROVEMENTS
The Guide Cane is currently not able to detect tabletops but it can
detect these objects with additional upward-looking sonars. The addition of these
sonars is expected to improve the Guide Cane’s performance to a level where a
visually impaired person could effectively use the device indoors. Outdoors,
however, the implementation of an additional type of sensor will be required to
allow the Guide Cane to detect important features, such as sidewalk border’s.
Dept. of AEI MESCE, Kuttippuram24
Seminar ’03 NavBelt and GuideCane
CONCLUSION
Both the Nav Belt and the Guide Cane are novel navigation aids designed
to help visually impaired users navigate quickly and safely through densely
cluttered environments. Both devices use mobile-robotics based obstacle-
avoidance technologies to determine in real-time, a safe path for travel and to
guide the user along that path. Theoretically, conveying to the user just a single
piece of information (i.e. a safe direction to walk in) is efficient, fast, and suitable
in practise to full walking speeds and even the image of a particular environment
could also be transmitted to the visually impaired person (image mode of Nav
Belt). It is fundamentally different from the existing ETA’s (Electronic Travel
Aids) that, at best, only inform the user about the existence and location of
obstacles but do not guide the user around them.
Dept. of AEI MESCE, Kuttippuram25
Seminar ’03 NavBelt and GuideCane
BIBLIOGRAPHY
NICHOLAS G.B., SYPROS T., “BIO-ENGINEERING
FOR PEOPLE WITH DISABILITIES”, IEEE JOURNAL, ROBOTICS
AND AUTOMATION – MARCH 2003.
I.ULRICH and J.BORENSTEIN, “VFH: LOCAL
OBSTACLE AVOIDANCE WITH LOOK AHEAD VERIFICATION”,
IEEE JOURNAL, ROBOTICS AND AUTOMATION – AUGUST
2000.
J.BORENSTEIN and Y.KOREN, “THE VECTOR FIELD
HISTOGRAM- FAST OBSTACLE- AVOIDANCE FOR MOBILE
ROBOTS”, IEEE JOURNAL, ROBOTICS AND AUTOMATION-
JUNE 2000.
Dept. of AEI MESCE, Kuttippuram26
Seminar ’03 NavBelt and GuideCane
CONTENTS
1. INTRODUCTION
2. MOBILE ROBOTICS TECHNOLOGY FOR THE VISUALLY IMPAIRERD
3. NAV BELT: -
OPERATIONAL MODES
ADVANTAGES
DISADVANTAGES
IMPROVEMENTS
4. GUIDE CANE
FUNCTIONAL DESCRIPTION
HARDWARE IMPLEMENTATION
MC68HC11
ADVANTAGES
DISADVANTAGES
IMPROVEMENTS
5. CONCLUSION
6. BIBLIOGRAPHY
Dept. of AEI MESCE, Kuttippuram27
Seminar ’03 NavBelt and GuideCane
ABSTRACT
Recent evolutionary achievements in robotics and bioengineering
have given scientists and engineers’ great opportunities and challenges to serve
humanity. With the development of radar and ultrasonic technologies over the
past four decades, when combined with the robotic technology and
bioengineering, gave rise to new series of devices, known as “electronic travel
aids (ETAs). It operates similar to a radar system, sends a laser or an ultrasonic
beam, which after striking the object reflects back and is detected by the
sensors, and so the corresponding distance from the object is calculated. In
particular, these devices are used to help people organ failure and people with
disabilities, such as visual impairment, deafness etc. This seminar is about an
instrument, which is the outcome of robotics and bioengineering, and it is
called “NavBelt and the GuideCane”. It is a robotics-based obstacle-avoidance
system for the blind and visually impaired.
NavBelt is worn by the user like a belt and is equipped with an array
of ultrasonic sensors. It provides acoustic signals via a set of stereo earphones
that guide the user around obstacles or “displays” a virtual acoustic panoramic
image of the traveller’s surroundings. One limitation of the NavBelt is that it is
exceedingly difficult for the user to comprehend the guidance signals in time to
allow fast walking.
A newer device, called GuideCane, effectively overcomes the above
problem faced by the use of NavBelt. The GuideCane uses the same mobile
robotics technology as the NavBelt but is a wheeled device pushed ahead of
the user via an attached cane. When the GuideCane detects an obstacle, it
steers around it. The user immediately feels this steering action and can follow
the GuideCane’s new path easily without any conscious effort.
Dept. of AEI MESCE, Kuttippuram28
Seminar ’03 NavBelt and GuideCane
ACKNOWLEDGEMENT
I extend my sincere gratitude towards Prof . P.Sukumaran Head of
Department for giving us his invaluable knowledge and wonderful technical
guidance
I express my thanks to Mr. Muhammed kutty our group tutor and
also to our staff advisor Ms. Biji Paul for their kind co-operation and
guidance for preparing and presenting this seminar.
I also thank all the other faculty members of AEI department and my
friends for their help and support.
Dept. of AEI MESCE, Kuttippuram29