Kwang-Joon Yoon

Designing a Biomimetic Ornithopter Capable of Sustained and Controlled Flight

We describe the design of four ornithopters ranging in wing span from 10 cm to 40 cm, and in weight from 5 g to 45 g. The controllability and power supply are two major considerations, so we compare the efficiency and characteristics between different types of subsystems such as gearbox and tail shape. Our current ornithopter is radio-controlled with inbuilt visual sensing and capable of takeoff and landing. We also concentrate on its wing efficiency based on design inspired by a real insect wing and consider that aspects of insect flight such as delayed stall and wake capture are essential at such small size. Most importantly, the advance ratio, controlled either by enlarging the wing beat amplitude or raising the wing beat frequency, is the most significant factor in an ornithopter which mimics an insect.

Thermal deformation analysis of curved actuator LIPCA with a piezoelectric ceramic layer and fiber composite layers

This paper reports thermal deformation analysis of LIPCA-C2 (Lightweight Piezo-composite Curved Actuator) that is lighter than other conventional piezo-composite type actuator. The LIPCA is composed of a piezoelectric ceramic layer which is sandwiched with composite layers having different CTE (coefficient of thermal expansion) and modulus. Due to the asymmetrical lay-up structure of LIPCA, an accurate analysis of thermally induced curvature is very important from the optimal design viewpoint. To investigate the thermal deformation behavior and the induced residual stresses of LIPCA-C2 at room temperature, the curvatures of LIPCA-C2 were measured and compared with those predicted based on the classical lamination theory.

Modeling of unmanned small scale rotorcraft based on Neural Network identification

Design and development of Unmanned Aerial Vehicles has attracted increased interest in the recent past. Rotorcraft UAVs, in particular have more challenges than its fixed wing counterparts. More research and experiments have been conducted to study the stability and control of RUAVs. A model-based control system design is particularly of our interest since it avoids a tedious trial and error process. To be able to successfully stabilize and control the RUAVs therefore a sufficiently accurate model is necessary. There are many methods in modeling small-scale rotorcraft. Using a standard first-principle based modeling approach, considerable knowledge about rotorcraft flight dynamics is required to derive the governing equation. Another method is system identification from flight data. This paper presents a method for system identification using Neural Networks. Input-output data are provided from nonlinear simulation of X-Cell 60 small scale helicopter. The data is used to train the multi-layer perceptron combined with NNARXM time regression input vector to learn nonlinear behavior of the vehicle.

Development of Bio-mimetic composite wing structures and experimental study on flapping characteristics

It has been over two years since we successfully develop our own design of flapping micro air vehicle with its dimension of 50cm. But more specified and detailed development to adopt the flight mechanism of natural flyers was required during downsizing its dimension. So this has driven us to the further research on efficient flight system especially on its wing structure. This paper explains our development of Bio-mimetic wing and experimental studies on flapping characteristics. By analysing each phase of flapping cycle, flapping characteristics of insect wing and mechanical wing could be compared. We focused our research to find out bio-mimetic wing of its performance : how exactly does it affect to the flapping efficiency. We also have reduced our flapping micro air vehicles weight from 45grams to less than 10grams and its size from 50cm to 15 cm. Although it hasnt been sufficient to fly in the field with the wind velocity over 2m/s, it still gives us the possibilities of mechanical flapping vehicle developed to be as small as insect. In order to become an autonomous ornithopter with capability of receiving data, such as vision, sound and temperature, we have taken every step that needed to have a high efficient flight mechanism as natures.

Development of Lightweight Piezo-composite Curved Actuator

This paper is concerned with the development, and performance test of LIPCA (Lightweight Piezo-composite Curved Actuator) that is lighter than other conventional piezo-composite type actuators. LIPCA is composed of top fiber composite layers with a high modulus and low CTE (Coefficient of Thermal Expansion), a middle PZT cermaic wafer, and base layers with a high modulus and high CTE. The performance of each actuator was evaluated using an actuator test system consisting of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system. The simply supported condition actuator was excited by the power supplier with 1.0Hz cycle and up to . The displacement at the center point of actuator was measured with non-contact laser displacement measuring system, It has been shown that the LIPCA-C2 can 34% decrease in mass and 13% increase in displacement compared to THUNDER.

An improved design of Piezo-Composite Actuator used as the artificial muscle for bio-inspired robots

During the past decade, lots of diverse researches have been conducted on application of smart materials to build small-scale robots. Several small, powerful, and reliable piezoelectric actuators using piezoelectric ceramic materials have been invented. Among them, LIPCA was introduced as the best unimorph actuator suitable for bio-inspired robots. The actuator plays the role as an artificial muscle which can produce up-and-down bending motion as voltage is applied. This paper presents an improved design of LIPCA (lightweight piezo-composite actuator) by using the direct piezoelectric effect along the poling direction (d33 mode) with interdigitated electrodes patterned on the two surfaces of PZT wafer that could help the new LIPCA enhancing the actuation performance considerably. An analytical model is used to give a comparison on the performance between the new design and the traditional LIPCA. Numerical optimization analysis on the design variables as electrode width, gap between electrodes and applied voltage for poling process is also performed.

Designing Cicada-Mimetic Flapping Wing with Composite Wing Structure and Application to Flapping MAV

This paper represents of the successful development on bio-mimetic wing design inspired from cicada. Since we have already developed the flapping MAVs with different scale having different performance, the attempts to design the wing structure similar to the insect wing, which expected to bring improvement of performance, were made. In this research, the cicada was chosen for the insect model and 36cm flapping MAV selected for wing application. The carbon fiber prepreg composite material was used for wing structure. The aerodynamic force measurement, wing kinematics observation and wind tunnel test were conducted to evaluate the performance between normal wing and bio-mimetic wing. It was proved that the bio-mimetic wing is superior to the normal wing in terms of not only force generation but also the aspect of appropriate wing kinematics. The force measurement of bio-mimetic wing in various wind flow velocity and operating power was also resulted to have better flight performance in lift and thrust coefficient comparing to the normal wing.

An experimental study to improve the performance of unimorph piezoelectric actuators subjected to external loading

This paper presents an experimental study to investigate the actuation performance of LIPCA (Lightweight Piezo- Composite unimorph Actuator) with different loading cases. High value of the manufacturing-induced compressive stress in PZT layer of LIPCA helps avoiding potential in-service failure, however, it may cause a reduction in strain due to the induced piezoelectric effect. High compressive prestress makes the domains aligned and constrained perpendicular to the stress direction. Consequently, fewer domains can be reoriented to contribute to polarization and strain output. The unimorph actuator is thus designed and operated such that the compressive stress in piezoceramic material is large enough to avoid failure in working condition but small enough to allow larger amount of non-180o domain switching. To compensate the high designed compressive stress state in the piezoceramic attention should be paid on the loading configuration when the actuator is working in-service condition. Experimental results show that the actuator should be arranged in a manner such that the stress state within the PZT wafer is in as more tension as possible to compensate the high compressive induced stress in the piezoceramic due to the manufacturing process.

Actuation characterization of the lightweight unimorph piezo-composite actuator for different loading cases

In this study, we focused on the actuation behavior of the lightweight piezo-composite unimorph actuator (LIPCA). Common loading configurations found in real applications of LIPCA have been studied including the center loading and tip loading cases. The domain switching effect that has strong influence on the performance of LIPCA was recorded. While a longitudinally compressed stress state within the PZT (lead zirconate titanate, Pb[Zr(x)Ti(1–x)]O3) layer in LIPCA is preferable to avoid failure during operation, experimental results showed that, for the transverse loading cases, the actuator should be arranged in a manner such that the stress state within the PZT is in as much tension as possible to encourage the non-180° domain switching. With investigated loading cases in this paper, suitable arrangements could help improve the actuation performance. The improvement can be up to almost 33% in simply-supported with center loading and 140% in clamped tip loading case.

Characteristic of an insect-mimicking flapping device actuated by a piezoceramic actuator

piezoceramic unimoph actuator can produce a relatively larger actuation force and actuation displacement when a proper compressive load is applied during operation, because the compressive stress causes material nonlinear behavior in the piezoceramic layer and triggers mechanical buckling. In this paper, we examined effects of the actuator under compression on the flapping angle and aerodynamic force generation capability. Effects of wing shape and passive wing rotation angle on the aerodynamic force production were also investigated. The average vertical force acquired by a 2D CFD simulation for an artificial wing showed a good agreement with the measured one by the experiment.