NAVBELT_AND_GUIDECANE

8/2/2019 NAVBELT_AND_GUIDECANE

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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 travellers 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 Canes 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.


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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 (ETAs),

was developed. This seminar introduces two novel ETAs that differ from the

ETAs 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.


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FIGURE 1


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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 robots

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).

NAV BELT

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 its concept.


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FIGURE 2


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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


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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 users 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

NavBelts sonars (a range of 120 and 3-mt radius). The binaural feedback


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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.


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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.


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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 users head orientation.

Adding more sonars to the front pack of the Nav Belt (pointing upwards and

downwards) can provide additional information.


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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 sonars 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).


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FIGURE 4


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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.


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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


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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 users of different height.

At the level of the users 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.


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FIGURE 5


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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

servos, 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 PCs 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.


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FIGURE 6


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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.


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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%.


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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 Familys

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.


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FIGURE 7


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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

developers hand. Figure 7 shows the GuideCane prototype which was

extensively tested at the University of Michigans Mobile Robotics Laboratory.


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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 Canes 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 borders.


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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 ETAs (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.


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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.


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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


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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 travellers 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 GuideCanes new path easily without any conscious effort.


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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.

NAVBELT_AND_GUIDECANE

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