Keeyoung Choi

Calibration of Inertial Measurement Units Using Pendulum Motion

The utilization of micro-electro-mechanical system (MEMS) gyros and accelerometers in low-level inertial measurement unit (IMU) influences cost effectiveness in a positive way under the condition that device error characteristics are fully calibrated. The conventional calibration process utilizes a rate table; however, this paper proposes a new method for achieving reference calibration data from the natural motion of pendulum to which the IMU undergoing calibration is attached. This concept was validated with experimental data. The pendulum angle measurements correlate extremely well with the solutions acquired from the pendulum equation of motion. The calibration data were computed using the regression method. The whole process was validated by comparing the measurement from the 6 sensor components with the measurements reconstructed using the identified calibration data.

Dynamic time responses of a flexible spinning disk misaligned with the axis of rotation

Using the finite element method, this study investigates the dynamic time responses of a flexible spinning disk of which axis of rotation is misaligned with the axis of symmetry. The misalignment between the axes of symmetry and rotation is one of major vibration sources in optical disk drives such as CD-ROM, CD-R, CD-RW and DVD drives. Based upon the Kirchhoff plate theory and the von Karman strain theory, three coupled equations of motion for the misaligned disk are obtained: two of the equations are for the in-plane motion while the other is for the out-of-plane motion. After transforming these equations into two weak forms for the in-plane and out-of-plane motions, the weak forms are discretized by using newly defined annular sector finite elements. Applying the generalized-α time integration method to the discretized equations, the time responses and the displacement distributions are computed and then the effects of misalignment on the responses and the distributions are analyzed. The computation results show that the misalignment has an influence on the magnitudes of the in-plane displacements. It is also found that the misalignment results in the amplitude modulation or the beat phenomenon in the time responses of the out-of-plane displacement.

Guidance algorithms for tactical missiles with strapdown seeker

Strapdown seekers have been recently adopted for short-range guided missiles to satisfy the demand for reducing the size and cost of guidance and control units. Since a strapdown seeker measures the look-angle only, rate gyros are additionally required for guidance command calculations. It is, however, well known that this kind of sensor combination inevitably includes a parasite loop which severely degrades the guidance performance. In this paper, we address how to design guidance algorithms to overcome problems due to the parasite loop. The performance of the proposed algorithms is investigated via numerical simulations for short-range tactical missiles.

A Study on Validation of OFP for UAV using Auto Code Generation

MATLAB Autocode generation is a feature that converts a block diagram model in Simulink to a c program. Utilizing this function makes MATLAB/Simulink an integrated developing environment, from controller design to implementation. It can reduce development cost and time significantly. However, this automated process requires high reliability on the software, especially the original Simulink block diagram model. And thus, the verification of the codes becomes important. In this study, a UAV flight program which is generated with Simulink is validated and modified according to DO-178B. As a result of applying the procedures, the final program not only satisfied the functional requirement but is also verified with structural point of view with Decision Coverage 93%, Condition Coverage 95% and MC/DC 90%.

Multi-vehicle formation using range-only measurement

This paper addresses how to make a formation of multiple unmanned aerial vehicles (UAVs) using only the relative range information. Since the relative range can easily be measured by an on-board range sensor like the laser range finder (LRF), the proposed method does not require any expensive and heavy wireless communication system to share the navigation information of each vehicle. Based on the two-dimensional (2-D) nonlinear equations of motion, we propose a nonlinear formation controller using the typical input-out feedback linearization method. The performance of the proposed formation controller is verified by various numerical simulations.

A path planning algorithm for Surveillance UAVs with timing mission constrains

In this paper, we propose a path generation algorithm with timing mission constrains in consideration of observing equipments, required observation time, line of sight, and flight capability of a UAV for effective ISR missions. The proposed algorithm is composed of the following steps: (1) targets modeling for LOS ranging, equipments performance, (2) the determination of target observation order the based on modified TSP(Travelling Salesman Problem) with time constraints, (3) the determination of line segments for target observation following target observation order, and (4) the generation Dubins curve for connecting line segments. Although the proposed method provides only a suboptimal solution, it is practical and produces a reference path for a UAV with ISR missions in almost real time.

Development of Servo Type Angle-of-Attack Sensor for UAV

A servo type angle of attack sensor using the null-seeking method is designed and its characteristics are analyzed in this study. Angle-of-attack in the null-seeking method is given by the probe rotation angle with respect to the body reference line when pressure difference measured in two holes on the probe becomes zero. This method provides highly accurate and uniform angle-of-attack measurements over all range. Hence, this kind of angle-of-attack sensor is adequate for unmanned aerial vehicles(UAVs). In this paper, we first analyze the requirements for developing angle-of-attack sensors. And the servo type angle-of-attack sensor is then designed and fabricated. The on-board angle-of-attack calculation algorithm is also developed. Finally, the characteristics of the developed angle-of-attack sensor are identified through MATLAB Simulink and wind tunnel tests.

Development of alpha sensor for unmanned aerial systems

An alpha sensor implies an angle of attack sensor to measure the angle between the aircraftpsilas reference line and the relative wind vector to the aircraft. Accurate measurements of AOA (angle-of-attack) are important to identify the aerodynamic coefficients and to evaluate the flight performance of an UAS. For a small scale UAS, AOA is usually estimated by AHRS (attitude heading reference system) combined with an GPS receiver, but this method provides poor information in general. In this paper, a null type alpha sensor developed by aerospace control and system Lab. in Inha University is introduced. The null type alpha sensor has many advantages compared with other kinds of alpha sensors. Most of all it has uniform error characteristics against AOA. And, as the speed increases, the sensor provides more accurate measurements.

Development of Ground Control Software for Operation of Multiple Unmanned Aerial Vehicles

Until recently, most of GCS(Ground Control Software) has been required to visualize attitude, position, status of vehicle and to transmit control and mission commands for a single UAV(Unmanned Aerial Vehicle). However, the GCS needs to expand its functions to handle more complex situations. Simultaneous operation of multiple UAVs is emerging as a new practice. Hence, we set up requirements for operation of multiple UAVs and suggest the architecture of GCS that satisfy the requirements. In this study, we analyze the upper requirements and define the total structure of GCS at first. Then we design the inner structure for requirements in detail. Finally, we verify the functions of GCS on PILS(Processor In the Loop Simulation) System.

A Study on Algorithm for Aircraft Collision Avoidance Warning

CFIT(Controlled Flight Into Terrain) is one of the major causes of aircraft accidents. In order to solve this problem, GPWS(Ground Proximity Warning System) is used to generate terrain collision warning using the distance between the aircraft and the underneath ground. Since the GPWS uses the vertical clearance only, it frequently generates false warnings. In this study, a terrain/obstacle collision avoidance warning algorithm was developed for fast flying and highly maneuvering fighters using the flight status and the geographic information. This algorithm condsiders the overall delay in the aircraft reactive motion including the pilot`s reaction time. The paper presents a detailed logic and test methods.