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In the past motion
trackers relied on a source or fixed point
to use as a reference. The fixed point
sends out an electronic signal to a receiver
on the person’s body (or visa versa) and the
unit can then triangulate the position of
the object in motion. This tracking
technique although quick and accurate
requires wires and is very expensive. It
also requires a fairly descent amount of
electronic equipment to support it. We are
in the process of designing a new compact
tracker.
The goal of the
new tracker is to integrate several tracking
technologies into a single circuit board
that will measure orientation in six degrees
or freedom and is sourceless i.e. it doesn’t
have any outside device that it references
to but references to itself.
Here are the types
of motion trackers that will be integrated:
-
ultrasonic
-
optical tracking
-
accelerometers
-
digital compass
-
digital gyro
Ultrasonic
trackers usually use a combination of
several transmitters and several receivers.
The sound returning from the transmitters
takes a certain amount of time to hit each
of the receivers and you can calculate
orientation in 6 axes. You can also measure
distance from a transmitter/receiver combo.
This way the device instantly knows how far
the walls are from it.
Optical
tracking uses a small camera that looks
at a single picture and selects bright
points or dark points in view. When the
next picture frame comes up it compares the
points that it had from the previous frame
and then updates the information of the
position of the tracker based on the
difference. While this is very accurate, it
is also very slow and requires a lot of
computing power to generate the data. If
this is used by itself, it can create lag
which can make someone nauseous. This type
of motion tracking is fairly new and cameras
have come way down in price.
Accelerometers
are inexpensive and are very fast. Their
use is becoming more common in devices. You
will find them in everything from Cell
phones to the new Wii controllers.
Accelerometers are great at determining the
start of a movement or motion. They tend to
drift but are responsive to quick motions.
The problem is that if they are moving in a
straight line, they do not sense the motion
as accurately.
A digital
compass works similar to a regular
compass and relies on the Earth’s magnetic
field. While these are great at determining
the rotation horizontal to the ground.
New digital compasses can also read in 3
axis of rotation.
A digital gyro
used to be fairly expensive but are now
dropping in price. The gyro can measure
it’s rotation in one of three axis. The
Trimersion uses a digital gyro. The gyros
tend to drift and can be finicky on the
initialization of the component but they are
very fast and are very small.
Motion tracking
and motion capture refer to a device that
can determine it’s orientation in two, three
or six axis of motion.
There are two
primary descriptions of motion trackers.
Sourced and sourceless. Sourced trackers
consist of two primary components: a known
fixed position and a moving target whose
position is referenced to the known
position. This provides accurate motion
data with few errors or “drift”.
Traditionally this technique has been
complex and expensive. Sourceless trackers
typically have no known fixed position and
are susceptible to drift or errors in data
that progressively get worse in time as the
device is tracked. Although sourceless
trackers have a tendency to drift, they are
usually the most inexpensive to
manufacture.
The proposed
sourceless motion tracker uses several
techniques to re-orient or re-align the
motion data with the goal of being as error
free as possible (minimum drift).
The proposed
device incorporates several well known
technologies into a single circuit board.
The goal is to produce a multi-purpose
sourceless tracking platform that could be
incorporated into any number of devices.
All of the technologies on the circuit would
or could work with each other through an
available software development kit. The
software on the board would compile data
from the various sensing devices to provide
a stream of six degree of freedom motion
orientation. The software would also have
the option of using any of the sensing
circuits or all of them in combination based
on the needs of the application. The
intelligent onboard analysis of the data
represented by each sensor should reduce
data positional error and because the
calculations are taking place on a dedicated
circuit board processor, should accelerate
the flow of data to connected computing
platforms.
So why all these devices?
We are working to
incorporate all of these techniques into a
single motion tracking device.
The gyro and
accelerometers give quick data. The data
can be compared and the average signal will
give very quick data with less drift. The
compass is slower but gives data to the gyro
and accelerometer stream that is very
accurate and is used as a reference for the
other techniques. Because the compass is
slower it will only be referenced and
compared as a corrective source for
everything else. The optical tracking is
the slowest form of tracking but the most
accurate when you are trying to overlay
computer images over the real world. To
provide tracking data while the optical
tracker is doing its calculations, the data
from the other devices kicks in keeping the
data flow constant. Lastly most of the
techniques above are great if the person is
standing still and only looking around but
when the person starts walking, none of them
provide quick accurate data about the
environment their in. This has been a huge
issue for us in the past and the main reason
we patented the ultrasonic sonar technique.
The ultrasonic gives you very quick and
accurate data about the person in relation
to the walls around him. Because the
measurements are so accurate, the data is
used as a reference for the optical and
accelerometer devices.
The unified sourceless tracker
will be a basic technology component that
can be incorporated into other devices. The
licensing potential of this is very
significant. One opportunity could be a toy
robot that navigates through hallways, a car
that adjusts steering or braking if it is in
a strange position, a miniature cell phone
or remote that can tell you where it is in
your house, or our purpose; to create a
video visor that knows where it is and what
position it is in anywhere without wires.
The ultimate goal is to do all of the
calculations and processing internally on
the circuit board and only sends out
positional or orientation data, real time to
the connected electronic device.
One technology
that has come down significantly in price
that should be investigated is Global
Positioning System (GPS). While this will
only help this device when it has a clear
track on four orbiting satellites, it will
give a better fixed position when measuring
distance over larger areas. GPS could
also be built into the design. |
