Design 6
Sensory perception for the blind
using Ultrasonic sensors
Assignment 4
Katelyn Sapio, Peter Okma, and Abhay Sampath
Group Participation
The group working on this project consists of Abhay Sampath (Team Leader), Peter
Okma, and Katelyn Sapio. The work for this report was split up evenly among the team
members. Katelyn Sapio wrote the sections on group participation, the introduction, the sensor
analysis, and the SWOT self-analysis. Abhay Sampath wrote the section on similar products that
already exist. He discusses the technologies used for these products, their advantages and
disadvantages, and compares them to our project idea. Peter Okma wrote the section on existing
technologies that could possibly be used for this product. He discusses what these technologies
are, how they can be used in this product, and what the advantages and disadvantages are of
each.
Introduction
According to Research to Prevent Blindness, there are 15 million visually impaired
people in the United States. This makes up almost 5% of the population. Even though this does
not seem like a large percentage, this is still a surprisingly large number of people.
People who are visually impaired have to overcome many obstacles in their everyday
lives. Because of this, there are many products out on the market to assist them in getting from
one place to another. These products utilize a wide range of technologies and each have their
advantages and disadvantages. The goal of this group is to create a product that optimizes all of
these features and truly makes everyday life a little easier for the blind.
This product will use ultrasonic sensors and the human ear to detect objects that could
become troublesome to a blind person. These sensors will be mounted in a headphone type
apparatus, two in the front and two in the back. These sensors will detect any objects
approaching the front or the back of the person wearing the device. The sensors will then trigger
a low beeping sound that will sound out of two sets of speakers, one in the front of each earpiece
and one in the back. This beeping noise will alert the user to the objects around them. For
example, if the beeping noise comes out of the back left speaker, the object is in the back left
direction of the user.
This device will also be able to alert the user to how close these objects are and, if these
objects are moving, how fast they are moving toward them. The ultrasonic sensors can
determine proximity and direction on their own but the velocity of the object can be determined
by taking data from the sensors a few times per second. The greater the distance change
detected, the faster the object is moving, taking into account the walking speed of the user (this
can be calibrated before use). These two parameters can be conveyed to the user using the
frequency and volume of the beeping tones. For example, the fast an object is moving, the more
beeps occur per second and the closer the object is, the louder the beeping sound.
Although this product will be implemented in a headphone type device, it is supplement
the users hearing ability, not obstruct it. For this reason, there will be a whole approximately ½’’
in diameter in the center of each ear piece so that the user can still clearly hear what is going on
around them.
Once the group decided on these initial idea parameters, they began research into
different technologies that can be used and similar products that already exist.
Choosing a sensor
The main component of this project is the ultrasonic sensors that will be mounted in the
ear piece. First, research was done into how ultra sonic sensors work. Basically, the sensor
emits a sonic pulse. This pulse bounces off of the objects in its path and send the pulse back to
the sensor. The time it takes the pulse to reach the sensor is used to determine the distance the
object is from the sensor. In this product, this will be used to determine the distance that an
object is from the user.
Unfortunately, ultrasonic sensors do have their limitations. For example, this sensor
cannot determine the different between objects of different size and it also cannot determine
direction. In order to fix this problem, two sensors are often used at a set distance from each
other. When one of the sensors has a higher reading than the others, the mechanism will know
that the object is closest to that sensor. In this product, this will allow the sensor to determine
what direction the object is in and relay this information back through the speakers.
After doing some research on ultrasonic sensors, the group found a web site that sells a
variety of different ultrasonic sensors. These sensors and their basic characteristics are listed in
Figure 1 below. Although we have not chosen a sensor yet, we have been weighing the
importance of the different characteristics.
First, this website separates sensors from indoor and outdoor sensors. While it is
important for this device to be precise, this product’s main use will be outdoors. This product
requires a sensor that will work well in rugged environments. Although there are two sensors
specified to be used outdoors, additional attachments can be added to the indoor sensors to
protect them from harsh conditions. All of the sensors appear to be both low cost and very small.
Size is very important because four of these sensors will need to fit on a headphones set.
The maximum range of the sensor is also very important. Since some objects may be
coming towards a blind person at a high velocity, the sensor needs to detect the object as soon as
possible so that the person will have enough warning that it is coming. The beam width is also
an important parameter. Since the user will generally be walking forward, it is more important
for the sensors in the front to be more accurate with the direction of the object. Because of this,
the sensors mounted on the back of the ear pieces can have a wider beam width than that of the
front sensors. Basically, the user just needs to know if there is something behind them. If
something seems odd, they can always turn around to get a better gauge. The sensors in the
front, however, need to be a little more accurate. The beam width would need to be narrower in
the front so that the user can more accurately detect what direction the approaching object is in.
Figure 1
There are many specifications that need to be considered when choosing sensors for this
product. Whatever we decide to go with, it seems like maxbotix.com will meet all of our needs.
SWOT Analysis
Strengths: This product could have a large impact in the way the visual impaired get
around. There is a chance that a product like this could become the norm in this market. It uses
inexpensive technologies to increase the easiness of mobility of the blind.
Weakness: Despite the impact that this product could have in the market, the actual
market for this product is rather small. Although there are a large number of visually impaired
people, if they are not blind, they might not want such a complex device.
Opportunities: There could also be a branch off of this project that makes finding
specific locations very simple. Marker devices could be placed on different locations that the
user would go to. For example, in the users workplace, his office, his boss’ office, the cafeteria,
or a common work area could all be marked. Sensors could be added that could sense these
locations and inform the user which marker they are approaching. In a broader sense, a GPS
type device could be added to the product to allow the user to detect locations farther away.
Markers could be placed on their home, their place of employment, their family’s homes, etc.
Threats: Ultrasonic sensors can be very risky for this type of application. The sensors
may not be able to detect two objects at once. A lot of testing would need to be done to
determine if this would be an effective method.
Competing Alternatives
Laser Cane
One of the most widely known assistive-mobility devices for the blind is the Laser Cane,
which uses laser light in conjunction with a camera and a computer processor to detect obstacles
and other hazards. The image is analyzed “as the user moves the device back and forth over a
scene.” Subsequently, one of three audio signals, each corresponding to a specific distance is
played.
This device requires too much processing, considering the only information being
conveyed to the user is an oversimplified distance reading. I could not find specific information
regarding range or accuracy, but because the device only chooses from three possible audio
signals, and range and accuracy are inversely proportional, our device has either a better range or
accuracy (or, more likely, both). In addition, Laser Cane has a large overhead in information
because the visual information gathered by the device is largely useless. It is stripped down until
only the distance can be used. This translates to a higher cost that isn’t offset by better
performance.
MOWAT Sensor
Another widely known device for blind mobility is the MOWAT Sensor. This is a small
device that uses ultrasonic waves to detect objects within a narrow beam width. If an object is
detected, the entire device vibrates. The rate of vibrations increases proportional to distance. This
device also has the limitation that it only corresponds to the nearest obstacle. The MOWAT
Sensor is very similar to the Polaron, which also detects obstacles within a range using ultrasonic
waves, and then vibrates.
While a vibrating device is a good supplement, it is quite difficult to associate certain
vibration rates with distances. In contrast, audio waves have been associated with memories and
meaning, either instinctively or through training.
Sensory 6
Sensory 6 is one of the alternatives that also uses audio to convey information. It is
intended to be a hands-free ultrasonic travel aid for the blind. Its main purpose is to extend the
user’s perception to include the environment beyond body space using the same principles as
radar.
Application to this Project
Our device is similar to Sensory 6 in principle, but in application, our device is much
more complex. For instance, one of the main differences is that our device has several sets of
sensors, some working in pairs. This generates a sense of direction in addition to the sense of
distance. Both are conveyed using the same audio signal, on which distance from the user is
conveyed as volume and velocity (relative to the user) is conveyed as pitch.
Laser Based Range Finder:
Laser based range finders provide an alternative solution to ultrasonic rangefinders.
Laser range finders can be used to recreate detailed 3D models in real time. Light detection and
ranging systems or LIDAR work in a similar fashion to ultrasonic sensors but have increased
precision. These systems use a high frequency infrared laser that sends out a large array of
pulses. A light detector senses the backscatter and real time and uses all the information to
construct and accurate sense of distance. There are two different ways this technology can be
used to produce 3D modes.
The first is scanning sensors. The laser range finding camera would be mounted to a
motorized device and would sweep in a predefined angle and creates a large range of input. This
input could be used to create a representation of the environment around the user. This
technique is similar to that used in Google’s autonomous car prototypes and would provide a
similar service in our product. This method does introduce some additional challenges. Moving
parts add increased complexity to a portable device.
A second solution allows for stationary sensors the project and array of pulses. . This
requires more computational power but provides a cheaper simpler solution. An example of this
technique has recently been incorporated into to Microsoft KINECT. This solution introduces
less complexity in the implementation but provides a smaller range and less accurate image
quality.
Both would provide increased image quality that would allow the systems to portray a
better representation of the environment to the user. The increases accuracy comes at the
expense of cost and complexity of the systems. A major problem could come from the increased
complexity of the algorithms needed as discussed in more detail bellow.
Software and Algorithms:
In our systems the sensors only provide one part of the solution. Ultimately they provide
use with some form of digital input that needs to be translated into an acoustic representation of
the data. Finding and implementing the right software provides the biggest challenge in
implementing the product. There are four considerations to take into account. 1) Complexity of
implementing solution, 2) How prone to error the system is 3) Can the system provides feedback
in real time 4) How much information is portrayed to the user.
One solution is to take the data from an ultrasonic sensor to detect how close an object is
. This data can be translated into an audible “beep” whose volume is repressive of how close the
nearest object is. This solution would be the easiest to implement, but provides a limited amount
of information to provide the user.
A second solution would be to do object identification. This solution would require a
detailed 3D image or a camera feed of the environment like that provided by a LIDAR sensor.
The software could detect objects in the environment based off their shape and provide detailed
audio queues such as “building to your right”. Well this solution seems the software would
require be limited by the object programmed in the database, would be difficult to code, and
provide large amounts of error.
The second solution is to use the image data and map generic “objects” these could be
detected via consecutive inputs tracking what comes close and farther to the sensor. All of this
information can be combined into a surround sound that could provide a clue of what objects are
where in the environment. This solution seems to provide a good compromise between
complexity and robustness.
Sources
http://classes.engr.oregonstate.edu/eecs/spring2003/ece44x/groups/g14/white%20papers/whitepaper
_matt.htm
http://www.maxbotix.com/MaxbotixHome.html
http://www.brailleinstitute.org/facts_about_sight_loss
Fast and robust tracking of multiple moving objects with a laser range finder
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=932853&tag=1
A comparison of line extraction algorithms using 2D laser rangefinder
http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1545234
Laser range finder based on synchronized scanners
http://www.opticsinfobase.org/abstract.cfm?&id=27938
Compact laser radar and three-dimensional camera
http://www.opticsinfobase.org/josaa/abstract.cfm?URI=josaa-23-4-800
http://www.tsbvi.edu/seehear/fall98/waytogo.htm
http://www.noogenesis.com/eta/current.html
http://www.agis.com/Eldercare-Basics/Assisted-Daily-Living-Aids/Mobility/Blind-MobilityAids/default.aspx
http://en.wikipedia.org/wiki/Blindness#Adaptive_techniques_and_aids
http://trid.trb.org/view.aspx?id=810306