pan-tilt repeatability value is 0.1° for a
travel range of 180°.
Calibration of the system to an external location using GPS coordinates
or some other method enables users to
determine true pointing accuracy. In
the absence of external calibration, it
is logical and acceptable to refer to the
repeatability of the pan-tilt positioner.
Angular resolution is the minimum
step size that the pan-tilt system can
move. For a high-performance
pan-tilt unit, minimum stepsize values on the order of
0.003° are possible. For low-cost pan-tilts, minimum step
sizes of 0.1° are typical. Some
pan-tilt units have adjustable
resolutions that are achieved
by micro-stepping the motors.
“smooths” motion and is par-
ticularly useful for long-range
imaging applications, such as
detecting vehicles or people
from 1 km or more for border security. If the pointing
resolution of the pan-tilt system is not sufficient for the application, there may be regions
the sensor or camera cannot
cover. This becomes more extreme as
range increases, as a certain angle of
motion equates to a longer radial distance at range.
Pan-tilt systems are complex electrome-
chanical devices. Their components all
affect pointing accuracy and repeatabil-
ity, including gears, belts, and reducers
that wear over time; homing or calibration systems that rely on limit sensors;
and housing or drive system rigidity
that contribute to error.
If the pan-tilt repeats the same pattern
in both axes on a predetermined scan
list, the preset locations will always be
approached from the same direction.
Pointing error from backlash or gear
wear may not be evident, as the gears
are always pre-loaded to the same side.
Applications requiring frequent di-
rection changes while tracking moving
objects may experience larger pointing
errors in the same system. In addition,
applications involving pointing in high
gusty winds will expose errors from
backlash in the pan-tilt system.
The repeatability of a pan-tilt system
can be observed if a target is approached
first from one direction and then from
the other. For example, if the system is
commanded to point to 90° in the pan
axis, it may approach from either the
left or the right. Any mechanical compliance or backlash in the gears will
contribute to the pointing error.
If errors are occurring in more than
one axis, then the overall error could
be larger. Consider if the error in one
axis is 0.15° and the error in the other is 0.1°, the reported position may be
off by 0.18°, which is the length of the
hypotenuse (a2 + b2 = c2). Uneven wear
or runout can also contribute to incon-
sistent pointing accuracies across differ-
ent areas of the axis.
Systems used in scientific research
may require correlation of position data
from the pan-tilt positioner with sensor data from the payload. These data
are collected using a laser rangefinder
or GPS, which can be highly accurate.
However, if the pan-tilt system is con-
stantly scanning and reporting position
data at a rate of 30 Hz or more, sys-
tem latency can contribute to perceived
error. This is because the pan and tilt
axes move before position and speed
information has time to reach the user.
With axis speeds of 120° per second or
higher, this perceived error will increase.
Timestamping of pan-tilt position
and speed data can compensate for latency errors. FLIR pan-tilt position and
speed data can be reported with internal
clock data from the controller board,
which runs at 90 MHz.
Pan-tilt positioners are commonly used for remote monitoring of construction sites,
fields, or critical infrastruc-
ture. When the system is au-
tomated, meaning an operator is not controlling the speed
and position, its success de-
pends on the ability of the
unit to point where it has been
In agricultural applications,
such as monitoring crop canopy temperature, a database
is built from collected images
to track temperature changes
over time and identify areas
that need attention (see Fig. 1).
A high degree of pointing error in the
pan-tilt positioner makes it impossible
to properly stitch together images or correctly reference locations. Similar sys-
tems for construction-site monitoring
also require a high degree of repeatabil-
ity—the ability to return to the same lo-
cation every time.
Pointing accuracy is also critical for
video tracking systems needed to ac-
curately target moving objects such as
UAVs or drones (see Fig. 2). Here, a camera system with one pan-tilt video tracker detects and locates the drone and a
second pan-tilt system with a frequency
jammer disrupts communications. In a
system with pan-tilt units for both the
video tracker and the jammer, speed ac-
curacy is critical. The speed at which
the camera tracks the drone must be
correct, or the system may not follow it
properly. The slaved pan-tilt must also
receive the correct speed information
FIGURE 2. A dual-camera pan-tilt system with frequency
jammer can be used to neutralize drones. (Courtesy of Black