Publisher’s Note: This paper, originally published on 9 October 2019, was replaced with a corrected/revised version on 20 February 2020. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
Nod-over-roll is a commonly used gimbal configuration especially in air-to-air missile seekers due to its volumetric advantage. It may further scaled down by implementing a folded optical layout and locating the detector off-gimbal. Yet, the concept suffers from an inherent kinematic singularity problem right at the center of its task space, where roll axis and pointing vectors coincide. The phenomenon is called zenith pass problem and has to be solved in real time for proper target tracking. A second drawback of the mentioned seeker structure is image registration problem, which reflects itself as rotation of constructed image on the FPA, and shall be considered while localizing the target. This work focuses on the kinematic analysis of the zenith pass and image registration problems in an air-to-air missile seeker perspective.
In order to orient aerial vehicles such as unmanned aerial vehicles and guided munitions toward intended target points, it
often becomes vital to acquire the correct information about the states of the targets during the flight of the vehicles. One
of the most widely-used ways to achieve this task is the utilization of seekers. Physically, the measurement capability of
seekers is restricted due to some physical, optical, and electronic limitations such as limited field-of-view (FOV),
atmospheric transmittance, and noise effects. Regarding these characteristics, basically two types of seekers are
employed in the relevant applications: strapdown or body-fixed seekers and gimbaled seekers. The strapdown seekers are
directly mounted on the considered vehicle body. Therefore, their measurements become relative to the body fixed
reference frame of the missile. For relieving the FOV limitations of the strapdown seekers, the gimbaled seekers are
preferred in some of the implementations. In this scheme, the seeker is mounted on a platform supported by two
orthogonal gimbals and stabilized by means of rate gyro feedbacks. This way, the FOV range of the seeker is increased
considerably. Also, the line of sight (LOS) angle and the LOS angular rate can be measured directly independently of the
missile motion. This study deals with the comparison of these two kinds of seekers according to certain criteria involving
mounting properties, FOV, angle and rate measurements, guidance method utilization, measurement methods, major
sources of measurement errors, and cost. A general evaluation is submitted at the end of the work.
Seekers are one of the most important subsystems of guided aerial munitions such that they are used both to detect and
track prespecified targets within specific engagement scenarios. Among them, infrared (IR) types constitute a significant
portion of seekers. Actually, performance characteristics of seekers depend on some certain factors. Regarding the type
of their sources, these factors can be classified as internal and external factors. Sensitivity, resolution, optics,detectors,
dome geometry, and materials happen to the most significant internal factors acting on the IR seekers while atmospheric
transmittance, and visibility can be counted within the remarkable external factors. In this study, the basic effects of the
above mentioned internal and external factors on the performance characteristics of a generic IR seeker is examined and
corresponding interpretations are presented at the end of the work.
This paper deals with the flap control of unmanned aerial vehicles (UAVs) using shape memory alloy (SMA) actuators
in an antagonistic configuration. The use of SMA actuators has the advantage of significant weight and cost reduction
over the conventional actuation of the UAV flaps by electric motors or hydraulic actuators. In antagonistic configuration,
two SMA actuators are used: one to rotate the flap clockwise and the other to rotate the flap counterclockwise. In this
content, mathematical modeling of strain and power dissipation of SMA wire is obtained through characterization tests.
Afterwards, the model of the antagonistic flap mechanism is derived. Later, based on these models both flap angle and
power dissipation of the SMA wire are controlled in two different loops employing proportional-integral type and neural
network based control schemes. The angle commands are converted to power commands through the outer loop
controller later, which are updated using the error in the flap angle induced because of the indirect control and external
effects. In this study, power consumption of the wire is introduced as a new internal feedback variable. Constructed
simulation models are run and performance specifications of the proposed control systems are investigated.
Consequently, it is shown that proposed controllers perform well in terms of achieving small tracking errors.
Considering the aerial surveillance and reconnaissance applications the use of infrared detectors gains importance. In this
scene, one of the primary issues that should be decided happens to be the operating range of the detectors. Namely, the
midwave and longwave ranges which are usually defined in the ranges of 3-5 and 8-12 μm, respectively, come into the
picture as viable alternatives. In this work, the basic properties of infrared detectors operating in midwave and longwave
regions are presented and then they are compared in terms of certain performance criteria. The study is concluded by a
The tests which are conducted to observe the behavior of a system in realistic operational conditions have great
importance in order to determine its performance prior to the relevant field studies. These studies provide the designers
with deciding on the necessary design updates and they also lead to reduce the total development cost in a significant
level. In order to execute the mentioned tests, the motion simulators being able to simulate the motion characteristics of
the system in a realistic environment are needed. Looking at the available simulators in the world, it is seen that different
system configurations have been used in accomplishing the desired test objectives. In these systems, not only the
mechanical designs differ from each other, but also the control systems are employed in various structures. In this study,
the properties of widely-used motion simulators designed for infrared camera systems are evaluated with regard of the
certain design issues. Also, their advantages and disadvantages are emphasized.
In guided munition applications, it is a priori to detect the intended target correctly and then to track it until the
termination of the engagement. However, especially high angular rates of the munition carrying an infrared (IR) type
camera cause the target image on the detector of the camera to blur. This, in turn, results in losing the correct target
information and even in missing the target. Therefore, it is required that the blur problem be handled carefully in an IRtype
camera design process. In this study, the blur problem of an IR-type gimbaled camera operating on a guided
munition is dealt with and the net field of view of the camera is determined for its different configurations. In the
calculations, the roll rate of the munition is taken into consideration because of the fact that it is much greater than its
counterparts in the yaw and pitch directions. Afterwards, the roll rate limit causing no blur is obtained and the ways that
can be applied to avoid this severe condition are proposed.