The future of unmanned aerial systems (UASs)
relies ultimately on safety. UAS safety is not merely measured by aircraft
performance and redundancies; it is measured by the ability for a system to operate
independently in an ever-changing, complex environment. The ability for a UAS
to autonomously sense and avoid obstacles increases the safety and provides a
method for safely operating in places that don’t receive GPS signal or places
that are not conducive to manual control (i.e. confined industrial spaces). The eXom UAS by senseFly Ltd. is one of the
most cutting edge fully automated UASs.
It is capable of automated flight without the use of GPS or pre-mapped
terrain databases. The system is extremely small, capable, and inexpensive.
Understanding the technology on this platform as well as integrating it in to
other small UASs can lead to an increase in safety standards for UASs in
general.
Sense and Avoid Operation and Sense and Avoid Technical Specifications
The eXom uses a multitude of sensors and
processors to accomplish its sense and avoid capability. The system is centered
on 5 dual-purposed modules that simultaneously measure both visual and
ultrasonic readings around the UAS. The dual-purpose modules are strategically
place around the airframe as well as above and below it in order to provide the
processor a full picture of the environment around the aircraft (senseFly Ltd.,
2015). The system works in two distinct ways. The ultrasonic sensors function
similarly to how bats use echolocation. The sensor sends out a specific
frequency of ultrasonic sound and then waits to here a return or echo from any
surface around it. This sensor can provide the system an accurate distance
measurement to the nearest obstacle. The ultrasonic sensor is suited to a task
such as maintaining a hover at a specific height and distance from an obstacle.
The visual portion of the sensor captures high definition photos of the areas
under the UAS and map out key points. Once these key points are captured, they
system autonomously measures drift, which is immediately corrected by the
precise autopilot carried onboard the system. In a demonstration provided by
the engineers, the system was not only able to hover in place, but was able to do
so without the use of GPS. The ultrasonic sensors were used to control the Z-axis
of motion and the visual sensors were utilized to control the X and Y-axis of
motion (senseFly Ltd., 2015).
Suitability for Small Unmanned Aerial Systems
The sensors that enable the eXom UAS to work
are also extremely light and inexpensive. A typical ultrasonic sensor used in
this system weighs only .003kg. Due to the need for multiple sensors, a five-sensor
system along with the required wiring and processor weighs in at only .024kg
(Perrett, 2014). Not only does this system weigh in at less than an ounce, but
a system crafted from off the shelf parts only cost about $140 to produce
(Perrett, 2014). The processing and power requirements of these types of
systems are also relatively small compared to the power requirements for flight
itself. The only difficulty in using ultrasonic sensors in rotorcraft-based
systems is the high amount of background noise produced by high-speed rotors.
To combat possible inaccurate readings, a buffer distance is used to ensure the
echo from the sensors is not drowned out by the echo of the rotors (Perrett,
2014).
A major significance of this technology is
that it can open up new fields to the small UAS world. This technology is
perfectly suited for industrial inspection purposes. This system can fly into
places that don’t typically receive GPS signal, as well into places that are
extremely cluttered and intricate. In the future, miniaturization of sense and
avoid system like that of the eXom could help the industrial sector save huge
amounts of money and down time because these micro UAS inspectors could get
deep into the guts of systems that would normally need to be turned off and
taken apart. Along with their application into the industrial world, these
sense and avoid systems could increase UAS safety and avoid dangerous and
costly accidents.
References
Perrett, J. (2014). Developing Sense
and Avoid (SAA) Capability in Small Unmanned Aircraft. Retrieved March 1, 2015,
from http://eprints.soton.ac.uk/366497/1/JPerrett Conference Paper.pdf
SenseFly Ltd. (2015). Learn More:
eXom. Retrieved March 1, 2015, from https://www.sensefly.com/drones/exom.html
