Laser Beam MicroMachining (LBMM) – A review

A survey of hybrid Unmanned Aerial Vehicles

This article presents a review on the platform design, dynamic modeling and control of hybrid Unmanned Aerial Vehicles (UAVs). For now, miniature UAVs which have experienced a tremendous development are dominated by two main types, i.e., fixed-wing UAV and Vertical Take-Off and Landing (VTOL) UAV, each of which, however, has its own inherent limitations on such as flexibility, payload, axnd endurance. Enhanced popularity and interest are recently gained by a newer type of UAVs, named hybrid UAV that integrates the beneficial features of both conventional ones. In this paper, a technical overview of the recent advances of the hybrid UAV is presented. More specifically, the hybrid UAV's platform design together with the associated technical details and features are introduced first. Next, the work on hybrid UAV's flight dynamics modeling is then categorized and explained. As for the flight control system design for the hybrid UAV, several flight control strategies implemented are discussed and compared in terms of theory, linearity and implementation.

A review on the platform design, dynamic modeling and control of hybrid UAVs

Intravascular stents were first introduced in the 1980s as an adjunct to primary angioplasty for management of early complications, including arterial dissection, or treatment of an inadequate technical outcome due to early elastic recoil of the atherosclerotic lesion. Despite the beneficial effects of stenting, persistent high rates of restenosis motivated the design of drug-eluting stents for delivery of agents to limit the proliferative and other inflammatory responses within the vascular wall that contribute to the development of a restenotic lesion. These strategies have yielded a significant reduction in the incidence of restenosis, but challenges remain, including incomplete repair of the endothelium at the site of vascular wall injury that may be associated with a late risk of thrombosis. A failure of vessel wall healing has been attributed primarily to the use of polymeric stent coatings, but the effects of the eluted drug and other material properties or design features of the stent cannot be excluded. Improvements in stent microfabrication, as well as the introduction of alternative materials may help to address those limitations that inhibit stent performance. This review describes the application of novel microfabrication processes and the evolution of new nanotechnologies that hold significant promise in eliminating existing shortcomings of current stent platforms.

/pdf/microfabrication-and-nanotechnology-in-stent-design-3v9tez166o.pdf

Microfabrication and nanotechnology in stent design.

Pulsed Nd:YAG laser cutting of NiTi shape memory alloys—Influence of process parameters

An optimal process of femtosecond laser cutting of NiTi shape memory alloy for fabrication of miniature devices

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.

https://iopscience.iop.org/article/10.1088/0964-1726/20/12/125007/pdf

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

http://enu.kz/repository/2009/AIAA-2009-5794.pdf

Control of a Hovering Mini Fixed Wing Aerial Vehicle

A systematic approach to characterize and control the attitude of a hovering tail-sitter mini-aerial vehicle (TS-MAV) is developed. A model of the TS-MAV dynamics is formulated by decoupling and linearizing a nonlinear model based on quaternions. Identification of the model parameters was carried out using a prediction error method and flight test data. Two control structures were synthesized to examine the benefits of using an anti-windup proportional-integral regulator in the inner control loop rather than in the outer control loop. It was found that a regulator in the inner loop reduced overshoot and eliminated an unstable pole. Flight tests with a TS-MAV test bed showed that a nine percent overshoot was reduced to zero thereby demonstrating the enhanced responsiveness of the vehicle using this control strategy.

https://journals.sagepub.com/doi/pdf/10.1260/1756-8293.2.4.211

Modeling and Control of a Hovering Mini Tail-Sitter:

Using nose-mounted micro-structures, it was shown experimentally and computationally in earlier publications by the authors that signiflcant side force could be generated at moderate angles-of-attack and for supersonic ∞ow on a generic missile conflguration. Under these ∞ow conditions, a \clean" slender body does not usually experience any lateral or side forces. In the current study, additional numerical simulations were performed in order to determine the mechanism by which the nose-mounted micro structures contribute to the generation of a side force at moderate angles-of-attack. The computational results show that the presence of the micro-structure on the nose contributes to the formation of a vortex that eventually merges with one of the two standard counter-rotating leeside vortices that form when a slender body is placed at angle-of-attack. The ∞ow efiector shed vortex being much stronger than the leeside ∞ow separation generated vortex, entrains the latter one to eventually merge into a single stronger vortex. The newly formed vortex, being stronger than the opposite side vortex, is forced to move upward above the missile’s leeside. In turn, this results in higher surface pressure on that side of the missile and hence the formation of a side force.

Franklin Wong

Papers

An optimal process of femtosecond laser cutting of NiTi shape memory alloy for fabrication of miniature devices

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

Control of a Hovering Mini Fixed Wing Aerial Vehicle

Modeling and Control of a Hovering Mini Tail-Sitter:

Side Force Generation Mechanism for a Missile with Nose-Mounted Micro-Structures