Nam Seo Goo

Design and manufacture of a lightweight piezo-composite curved actuator

In this paper we are concerned with the design, manufacture and performance test of a lightweight piezo-composite curved actuator (called LIPCA) using a top carbon fiber composite layer with near-zero coefficient of thermal expansion (CTE), a middle PZT ceramic wafer, and a bottom glass/epoxy layer with a high CTE. The main point of the design for LIPCA is to replace the heavy metal layers of THUNDER™ by lightweight fiber reinforced plastic layers without losing the capabilities for generating high force and large displacement. It is possible to save up to about 40% of the weight if we replace the metallic backing material by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use an epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a carbon prepreg were simply stacked and cured at an elevated temperature (177 °C) after following an autoclave bagging process. We found that the manufactured composite laminate device had a sufficient curvature after being detached from a flat mould. An analysis method using the classical lamination theory is presented to predict the curvature of LIPCA after curing at an elevated temperature. The predicted curvatures are in quite good agreement with the experimental values. In order to investigate the merits of LIPCA, performance tests of both LIPCA and THUNDER™ have been conducted under the same boundary conditions. From the experimental actuation tests, it was observed that the developed actuator could generate larger actuation displacement than THUNDER™.

Effect of an Artificial Caudal Fin on the Performance of a Biomimetic Fish Robot Propelled by Piezoelectric Actuators

This paper addresses the design of a biomimetic fish robot actuated by piezoceramic actuators and the effect of artificial caudal fins on the fish robot’s performance. The limited bending displacement produced by a lightweight piezocomposite actuator was amplified and transformed into a large tail beat motion by means of a linkage system. Caudal fins that mimic the shape of a mackerel fin were fabricated for the purpose of examining the effect of caudal fin characteristics on thrust production at an operating frequency range. The thickness distribution of a real mackerel’s fin was measured and used to design artificial caudal fins. The thrust performance of the biomimetic fish robot propelled by fins of various thicknesses was examined in terms of the Strouhal number, the Froude number, the Reynolds number, and the power consumption. For the same fin area and aspect ratio, an artificial caudal fin with a distributed thickness shows the best forward speed and the least power consumption.

Development and application of conducting shape memory polyurethane actuators

This paper presents the development and application of conducting shape memory polyurethane (CSMPU) actuators. While conventional shape memory polyurethanes were activated by an external heat source, the conducting shape memory polyurethanes, introduced in 2004, are activated by electric power. CSMPU actuators were manufactured by adding carbon nano-tubes to conventional shape memory polyurethane. The main problem of the previous CSMPU was poor dispersion of carbon nano-tubes. In this paper, we tried to solve the dispersion problem, and after a lot of elaborate work CSMPU actuators with better electrical characteristics were fabricated with in situ polymerization. Then the actuation performance of the CSMPU actuators was also measured and assessed. Finally, the possibility of applications was examined through the installation of a CSMPU actuator in a micro air vehicle.

Characteristics of a Beetle's Free Flight and a Flapping-Wing System that Mimics Beetle Flight

In this work, we first present a method to experimentally capture the free flight of a beetle (Allomyrina dichotoma), which is not an active flyer. The beetle is suspended in the air by a hanger to induce the free flight. This flight is filmed using two high-speed cameras. The high speed images are then examined to obtain flapping angle, flapping frequency, and wing rotation of the hind wing. The acquired data of beetle free flight are used to design a motor-driven flapper that can approximately mimic the beetle in terms of size, flapping frequency and wing kinematics. The flapper can create a large flapping angle over 140° with a large passive wing rotation angle. Even though the flapping frequency of the flapper is not high enough compared to that of a real beetle due to the limited motor torque, the flapper could produce positive average vertical force. This work will provide important experience for future development of a beetle-mimicking Flapping-Wing Micro Air Vehicle (FWMAV).

Three-dimensional cure simulation of composite structures by the finite element method

In this paper, a finite element formulation for three-dimensional cure simulation of composite structures is introduced and a three-dimensional finite element code is developed based on the formulation. Results from the present cure simulations agreed well with the measured cure-induced temperatures and the numerical results from one- or two-dimensional simulations. Unlike in the one- and two-dimensional simulations, temperature and degree of cure can be calculated at any point within composite structures in the present analysis. The finite element program can be used for cure simulation of composite structures with arbitrary geometry under non-uniform autoclave temperature distribution.

Stable Vertical Takeoff of an Insect-Mimicking Flapping-Wing System Without Guide Implementing Inherent Pitching Stability

We briefly summarized how to design and fabricate an insect-mimicking flapping-wing system and demonstrate how to implement inherent pitching stability for stable vertical takeoff. The effect of relative locations of the Center of Gravity (CG) and the mean Aerodynamic Center (AC) on vertical flight was theoretically examined through static force balance consideration. We conducted a series of vertical takeoff tests in which the location of the mean AC was determined using an unsteady Blade Element Theory (BET) previously developed by the authors. Sequential images were captured during the takeoff tests using a high-speed camera. The results demonstrated that inherent pitching stability for vertical takeoff can be achieved by controlling the relative position between the CG and the mean AC of the flapping system.

Design and demonstration of a biomimetic wing section using a lightweight piezo-composite actuator (LIPCA)

This paper describes the design and evaluation of biomimetic wing sections, where the trailing edges of the wing sections are actuated by the piezoceramic actuator LIPCA (lightweight piezo-composite actuator). Thermal analogy based on linear elasticity was used for the design and analysis of the wing sections. In the actuation test of the wing sections, the effective deflection angle of the trailing edge was approximately five degrees at 300 V input. The predicted and measured actuation displacements agreed very well up to an input of 150 V. However, the real actuation displacement became larger than the estimated value for higher input voltages due to the material non-linearity of the lead zirconate titanate (PZT) wafer in the LIPCA. The biomimetic wing sections can be used for control surfaces of small scale unmanned aerial vehicles (UAVs).

Use of a digital image correlation technique for measuring the material properties of beetle wing

Beetle wings are very specialized flight organs consisting of the veins and membranes. Therefore it is necessary from a bionic view to investigate the material properties of a beetle wing experimentally. In the present study, we have used a Digital Image Correlation (DIC) technique to measure the elastic modulus of a beetle wing membrane. Specimens were prepared by carefully cutting a beetle hind wing into 3.0 mm by 7.0 mm segments (the gage length was 5 mm). We used a scanning electron microscope for a precise measurement of the thickness of the beetle wing membrane. The specimen was attached to a designed fixture to induce a uniform displacement by means of a micromanipulator. We used an ARAMIS™ system based on the digital image correlation technique to measure the corresponding displacement of a specimen. The thickness of the beetle wing varied at different points of the membrane. The elastic modulus differed in relation to the membrane arrangement showing a structural anisotropy; the elastic modulus in the chordwise direction is approximately 2.65 GPa, which is three times larger than the elastic modulus in the spanwise direction of 0.84 GPa. As a result, the digital image correlation-based ARAMIS system was successfully used to measure the elastic modulus of a beetle wing. In addition to membrane’s elastic modulus, we considered the Poisson’s ratio of the membrane and measured the elastic modulus of a vein using an Instron universal tensile machine. The result reveals the Poisson’s ratio is nearly zero and the elastic modulus of a vein is about 11 GPa.

A nine-node assumed strain shell element for analysis of a coupled electro-mechanical system

In the present paper, the formulation of a nine-node assumed strain shell element is modified and extended for use in analysis of actuator-embedded structures. The shell element can alleviate locking and has six degrees of freedom (DOFs) per node as a result of discarding the assumption of no thickness change. Mechanical–piezoelectric DOFs are coupled through the constitutive equation and the electric potential is assumed to be linear through the thickness of a piezoelectric layer. A finite-element program based on the formulation is generated and the code is validated though solving typical numerical examples. The results from the present work agree well with those from other references.

Measurement of Force Produced by an Insect-Mimicking Flapping-Wing System

We present a new version of a compact insect-mimicking flapping-wing system driven by a small motor, and suggest two testing approaches to measure the thrust or lift generated by a flapping-wing system. Flapping performance tests show the proposed flapping-wing system, which is powered by an onboard battery (lithium, 3.7 V, 180 mAh), could flap at flapping frequency of 25 Hz, and produce an average thrust or lift of about 3 g. In a wired-flight test under constrained conditions, the flapping-wing system could fly at an average forward velocity of 700 mm·s−1. For measuring the average thrust or lift produced by the flapping-wing system, we propose two testing approaches of wired-flight test and swing test with the aid of a high-speed camera and they are compared with a load cell measurement. The average thrust or lift values from the two proposed approaches agree well with the average thrust or lift values measured by a load cell.