Navbelt and guide cane

7/29/2019 Navbelt and guide cane

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ACKNOWLEDGEMENT

I express my gratitude to our institution NALLA MALLA REDDY ENGINEERING

COLLEGE, and our beloved principal Dr. Divya Nalla for providing me the means of attaining

most cherished goals.

I extend my sincere gratitude towards Prof. Ram Chandra Head of Department

Electronics And Communication Engineering for giving me the opportunity to present this

technical seminar.

I express my gratitude to Mr. Mahesh sir for his kind co-operation and guidance for

preparing and presenting this seminar.

I also thank all the other faculty members of ECE department and my friends for their

help and support.


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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 aroundobstacles 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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CONTENTS

1. INTRODUCTION 04

2. NAV BELT 05

OPERATIONAL MODES 08

ADVANTAGES DISADVANTAGES 08

IMPROVEMENTS

3. GUIDE CANE

FUNCTIONAL DESCRIPTION 08

HARDWARE IMPLEMENTATION 10

MC68HC11 12

ADVANTAGES 14 DISADVANTAGES 14

IMPROVEMENTS 14

4. CONCLUSION 15

5. REFERENCES 16


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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 computerized devices based on advanced mobile

robotic navigation for obstacle avoidance useful for visually impaired people. This is

Bioengineering forpeople 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 patheasily 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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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 (1),

shows the experimental prototype of the device and pictorial representation of its concept.

FIGURE 1

A binaural feedback system based on internal time difference (i.e. the phase difference betweenthe left and right ears) and amplitude difference (i.e. the difference in amplitude between the two


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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 recommendedtravel 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 traveldirection 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 importantparameter 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 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 systemselects 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 theobstacle 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 thenavigation 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 headfrom 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). Thebinaural feedback 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 (2) shows the graphical

representation of the image mode.


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Figure 2

a) Obstacles are detected by ultrasonic sensorsb) Sonar range readings are projected on to the polar histogramc) An acoustic sweep is generated from the polar histogram

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 distancefrom 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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ADVANTAGES1. NavBelt can detect objects as narrow as 10mm.2. NavBelt can reliably detect objects with a diameter of 10cm or more,

regardless of the travel speed.

3. The current detection range of the NavBelt is set for 3mt.

DISADVANTAGES

1. For object with diameter of 10mm, the detection is possible if the objects are stationaryor the subject is walking slowly (less than 0.4 m/s).

2. 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.3. It does not allow fast-motion.4.

The NavBelt uses a 2-D representation of the environment. The representation of this typebecomes 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 beremoved 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.

GUIDE CANE

It can be thought of as a robotic guide dog. The functional components of the GUIDECANE 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 isequipped 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 oftravel and as soon as this direction is


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free of obstacles, steers the wheels to the left until the 90 left turn is completed. Functional

components are shown in figure (3).

FIGURE 3

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 theObstacle Avoidance Algorithm prescribes an alternative direction to circumnavigate the


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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, thetraveller 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 detectedin 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 tostop. 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 (3) alsoshows the way GuideCane avoids the obstacles.

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, theelectronic 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 (4) shows the mechanical hardware of the GuideCane. Itconsists 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 inthe front in a semicircular fashion with an angular spacing of 15, thereby covering a 120 sectorahead 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 issteered 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: -


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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 microprocessorclocked 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(4) also shows the electronic hardware.

FIGURE 4: The guide cane system. Dashed lines indicate components that are required onlyrequired during the development stage.

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


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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, whichperforms 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 microcontrollers, 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 (5) shows the connections of

MC68HC11.

FIGURE 5

ARCHITECTURE


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The MC68HC11 is optimized for low power consumption and high-performance

operation at but frequencies up to 4 MHz The CPU has two 8-bit accumulators (A&B) thatcab 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, andinstructions are provided for stack manipulation. Typically multiplexed address and data bus.

Other features include: -

o Powerful bit-manipulation instructions.o Five powerful addressing modes (Immediate, Extended, Indexed, Inherent and

Relative).

oPower saving STOP and WAIT modes.

o Memory-mapped I/O and special functions.

Serial Communications Interface (SCI): -

The SCI features a full duplex Universal Asynchronous Receiver/Transmittersystem, 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 continuouswaveforms with programmable rates and software selectable duty cycles from 0 to 100%.

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


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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 ofuse. 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. TheA/D is software programmable to provide single or continuous conversion modes. 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 canbe 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 LCDscreen that is attached to the handle below the developers hand.

ADVANTAGES1. It allows fast walking, up to 1m/s while completing complex maneuvers through

cluttered environments.

2. It can be used to travel or detect staircases.3. Easy to handle, and no extensive training needed.4. It rolls on wheels that are in contact with the ground, thus allowing position estimation

by odometry.

DISADVANTAGES

1. It uses ultrasonic sensor-based obstacle avoidance system, which is not sufficientlyreliable at detecting all obstacles under all conditions.

2. It cannot detect overhanging objects like tabletops.

IMPROVEMENTSThe 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 thedevice 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.

CONCLUSION


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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. Bothdevices 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

practice to full walking speeds and even the image of a particular environment could also betransmitted 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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REFERENCES

1. GOOGLE IMAGES2. BIO-ENGINEERING FOR PEOPLE WITH DISABILITIES, IEEE JOURNAL,3. http://www.123helpme.com/sound-navigation-and-ranging-sonar4. VFH: LOCAL OBSTACLEAVOIDANCE WITH LOOK AHEAD VERIFICATION,

IEEE JOURNAL

5. www.advancedmsinc.com/
http://www.123helpme.com/sound-navigation-and-ranging-sonarhttp://www.123helpme.com/sound-navigation-and-ranging-sonarhttp://www.123helpme.com/sound-navigation-and-ranging-sonar

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Navbelt and guide cane