Franklin Wong

Design and verification of a smart wing for an extreme-agility micro-air-vehicle

A special class of fixed-wing micro-air-vehicle (MAV) is currently being designed to fly and hover to provide range superiority as well as being able to hover through a flight maneuver known as prop-hanging to accomplish a variety of surveillance missions. The hover maneuver requires roll control of the wing through differential aileron deflection but a conventional system contributes significantly to the gross weight and complexity of a MAV. Therefore, it is advantageous to use smart structure approaches with active materials to design a lightweight, robust wing for the MAV. The proposed smart wing consists of an active trailing edge flap integrated with bimorph actuators with piezoceramic fibers. Actuation is enhanced by preloading the bimorph actuators with a compressive axial load. The preload is exerted on the actuators through a passive latex or electroactive polymer (EAP) skin that wraps around the airfoil. An EAP skin would further enhance the actuation by providing an electrostatic effect of the dielectric polymer to increase the deflection. Analytical modeling as well as finite element analysis show that the proposed concept could achieve the target bi-directional deflection of 30° in typical flight conditions. Several bimorph actuators were manufactured and an experimental setup was designed to measure the static and dynamic deflections. The experimental results validated the analytical technique and finite element models, which have been further used to predict the performance of the smart wing design for a MAV.

Control of a Hovering Mini Fixed Wing Aerial Vehicle

This paper describes an approach for designing a stabilizing control strategy of a mini fixed wing aerial vehicle in hovering mode. This flight mode gives the ability to navigate inside a constrained environment. An inertial measurement unit is used to measure the attitude. The increased mass due to the on-board sensor poses a greater challenge to developing a functional autonomous vehicle than previous studies that employed o-board sensors for attitude sensing. Linear transfer functions are proposed for attitude with slow transits modeling. The design is achieved with a frequency domain method involving the Nichols chart. The control of a hovering vehicle requires ecient tuning methods capable of insuring robustness to account for model errors. Simulation and flight test results are presented to show the performance obtained with the proposed tuning method.

Attitude Estimation and Control of a Hovering Mini Aerial Vehicle

This paper presents the flight performance obtained by a mini fixed wing air vehicle that is equipped with an on-board embedded system running simple control and non-commercial attitude estimation algorithms that process positional data from low-cost sensors. A complementary filter based on quaternions was implemented. Data from three-axis accelerometers and rate gyros were used for attitude estimation while a range-finder sonar was used for altitude measurement. Proportional-integrator-derivative regulators were selected for attitude and altitude control. Controller tuning was achieved using a frequency domain method based on the Nichols chart. Flight testing of the control hardware and algorithms showed that body attitudes could be maintained within 3 of the desired setpoint and that the vehicle altitude could be maintained within 10cm of the desired altitude with a decoupler.

Enhancement of YBCO microbolometer performances with regionally thinned microbridges

Silicon nitride microbridges (50x50 mm2, 0.6 mm thick), suspended over a silicon substrate, were patterned and thinned. These patterns consist of 2 to 12 windows that were thinned to approximately 0.3 mm. Microbolometers were fabricated by sputtering a YBaCuO thin film over the bridges. The experimental results showed that the regionally thinned microbridges have a lower thermal time constants t (about 1.6 ms) than that of the standard pixel configuration (2.6 ms). On the other hand, the fact that the regionally thinned microbolometers having detectivity D* values comparable to or even six times superior than that of the standard pixel showed that the decrease in response time is not penalized by loss of detection performance. The simulation results also show that as the amount of material removed is increased, the thermal time constant drops significantly while the (τ/G)1/2 ratio (where G is the thermal conductance of the pixel) only decreases slightly, suggesting that the reduced response time will not cause a significant drop in detectivity D*. The simulation results of mechanical integrity show that a specific regionally thinned microbridge design has 22 % higher stiffness than that of a standard pixel design with similar thermal properties. The fact that thick regions remained on the regionally thinned pixels (like the edges of the pixels) provide significant mechanical support to the microstructures. This confirms the validity of the regionally thinned microbridges approach.

GPS-based attitude determination using RLS and LAMBDA methods

This work presents a procedure for getting 3D attitude from GPS raw measurements. The method is based on differential GPS and uses four receivers; although it can be easily generalized. The disposition of the receivers is fixed in the body frame, as attached to a rigid platform that moves freely in the local navigation frame. Baseline estimation is performed through a Recursive Least Squares (RLS) algorithm using code and carrier phase measurements. This work is an extension to the work of Chang et al. (2005) to multiple roving receivers, and where the LAMBDA method has been used for integer ambiguity resolution. The dispositions of receivers are known a priori, and this information used to constrain the solution at each epoch. Finally, 3D attitude is determined from the estimated baselines using the SVD method. The performance of the proposed method is evaluated through simulation. The results show significant enhancement with respect to the original method as well as with comparison with previous work in literature.

Relative Localization for Small Wireless Sensor Networks

In this paper, we investigate relative localization techniques based on internode distance measurements for small wireless networks. High precision ranging is assumed, which is achieved by using technologies such as ultra-wide band (UWB) ranging. A number of approaches are formulated and compared for relative location estimation, which include the Linear Least Squares (LLS) approach, the Maximum Likelihood Estimation (MLE) approach, the Map Registration Approach (MAP), the Multidimensional Scaling (MDS) approach and the enhanced MDS approaches. Finally, computer simulations are used to compare the performances and effectiveness of these techniques, and conclusions are drawn on the suitability of the relative localization techniques for small networks.