A bioinspired MAV with nanocomposite wings and flexure joints: design and structural dynamic analysis

Compliant mechanisms are single-piece flexible structures that deliver the desired motion by undergoing elastic deformation as opposed to jointed rigid body motions of conventional mechanisms. Compliance in design leads to jointless, no-assembly (Fig. 1), monolithic mechanical devices and is particularly suited for applications with small range of motions. The compliant windshield wiper shown in Fig. 1 illustrates this paradigm of no-assembly. Conventional flexural mechanisms employ flexural joints that connect relatively rigid links as depicted in Fig. 2. Reduced fatigue life, high stress concentration and difficulty in fabrication are some of the drawbacks of flexural joints. Our focus is on designing compliant mechanisms with distributed compliance which employs flexural links (see Fig. 3) and have no joints (neither pin nor flexural joints) for improved reliability, performance, and ease of manufacture. Distributed compliant mechanisms derive their flexibility due to topology and shape of the material continuum rather than concentrated flexion at few regions. This paper focuses on the unique methodology employed to design jointless mechanisms with distributed compliance. The paper also illustrates a compliant stroke amplification mechanism that was recently designed, fabricated and tested for MEMS application.

In recent years, many efforts have been made to exploit full-field measurement optical techniques for modal identification. Three-dimensional digital image correlation using high-speed cameras has been extensively employed for this purpose. Modal identification algorithms are applied to process the frequency response functions (FRF), which relate the displacement response of the structure to the excitation force. However, one of the most common tests for modal analysis involves the base motion excitation of a structural element instead of force excitation. In this case, the relationship between response and excitation is typically based on displacements, which are known as transmissibility functions. In this study, a methodology for experimental modal analysis using high-speed 3D digital image correlation and base motion excitation tests is proposed. In particular, a cantilever beam was excited from its base with a random signal, using a clamped edge join. Full-field transmissibility functions were obtained through the beam and converted into FRF for proper identification, considering a single degree-of-freedom theoretical conversion. Subsequently, modal identification was performed using a circle-fit approach. The proposed methodology facilitates the management of the typically large amounts of data points involved in the DIC measurement during modal identification. Moreover, it was possible to determine the natural frequencies, damping ratios and full-field mode shapes without requiring any additional tests. Finally, the results were experimentally validated by comparing them with those obtained by employing traditional accelerometers, analytical models and finite element method analyses. The comparison was performed by using the quantitative indicator modal assurance criterion. The results showed a high level of correspondence, consolidating the proposed experimental methodology.

In this study, the damage identification procedure combining the advantages of high-speed 3D digital image correlation (DIC) that is used for modal analysis and wavelet-based processing algorithm is presented. The proposed procedure has been successfully validated on sandwich composite structures with internal damage of a core and impact damage, and its performance was demonstrated by detection, localisation, and identification of shapes of damage in tested structures, comparable to the results from scanning laser Doppler vibrometry (SLDV). The effectiveness in damage identification was achieved by the development of processing algorithm of acquired mode shapes, which uses a 2D double-density directional wavelet transform with increased sensitivity with entropic weights allowing to automatically select those wavelet coefficients and mode shapes, which are most sensitive to damage. The procedure presented in this paper demonstrates the performance of 3D DIC for damage identification as a cost-effective alternative to the procedures based on SLDV measurements.

When combined with high-speed photography technology, the digital image correlation (DIC) method provides an excellent photographic image processing capability that can be used to convert the evolving full-field surface properties of structures to sets of two-dimensional (2D) or three-dimensional (3D) coordinate values. In this study, the applicability of the DIC method and high-speed cameras in underground mining was investigated by measuring the displacement and vibration of rock pillars caused by blasting. This technique is used extensively in engineering and is increasingly being applied to new fields. As a result of comparing the DIC results for blast vibration with the measured values of the contact sensor through field tests, the maximum displacement and vibration speed were found to be 86% and 93% accurate, respectively. In addition, the obtained values appeared similar to those predicted through numerical analysis. Field test results indicate that both methods yielded similar results. Therefore, it is concluded that it is feasible to use the DIC and high-speed camera to measure ground displacements and vibrations from blasting in underground mining. In addition, the system conditions required for blast vibration measurement were considered by comparing the accuracy with the existing measurement methods.

This paper develops a simple flapping wing mechanism fabricated monolithically from an epoxy-based negative photoresist (SUEX) dry film. The developed fabrication process has fewer steps compared to other methods, does not use precious metals, and greatly reduces processing time and cost. It simultaneously defines the pico air vehicle (PAV) airframe, compliant flapping mechanism, and artificial insect wing using photolithography. Using this process, we designed and fabricated the LionFly, a flapping wing mechanism actuated by a PZT-5H bimorph actuator. Rapid prototypes were fabricated with precisely defined features and material properties and geometry that are similar to insects. We present the fabrication process and characterization of SUEX and show that flexure thickness can be controlled by 310 nm UV dose. Static and dynamic modeling of the LionFly have excellent agreement with experimental data. Performance from multiple prototypes shows devices with resonance frequency of 49.13 ± 1.43 Hz and up to 75° peak to peak flapping angle demonstrating applicability of the fabrication process for flapping wing PAV applications.

Flapping Wing Micro Aerial Vehicle (MAV) is the development of Unmanned Aerial Vehicle (UAV) which is smaller and lighter. GaneFly is a flapping wing MAV robot developed in this paper. GaneFly flying platform is designed to be able to fly with flapping mechanism that adapts the flapping wing of the dragonfly and also designed to be able to turn and pitch according to the input command. Design of the GaneFly platform includes the selection and design of mechanical, electrical components, and integration between mechanical and electrical component. Selection of components and materials primarily in the small dimensions and lightweight but still considering the performance. The design of the mechanical adapts to the existing research of the flapping wing MAV. The result of the design is integrated parts with electrical components up to be a flying platform. After going through various processes of trial and repair, the GaneFly platform can fly with its flapping mechanism and can be controlled quite well.

The first natural frequency directly affects the operational conditions of compliant mechanisms in precision engineering systems. To address this challenge, a computational method based on the surface response method is proposed to optimize the frequency of a new one degree of freedom (DOF) compliant mechanism. Initially, a 1-DOF 3D model of a compliant mechanism is built. The dynamic equation and the frequency response are formulated via equivalent stiffness and the Lagrange method. Subsequently, a series of numerical simulations are conducted to find the fundamental frequency of the mechanism. The initial dimensions of the flexible joints are determined, and the initial frequency is analyzed by using finite element analysis. Next, the flexible joints in the designed mechanism are optimized by a variant of the genetic algorithm. The optimized dimensions of the mechanism are found with the thickness of the circular joint of 1.10 mm, the thickness of the leaf joint of 1.19 mm, and the length of the leaf joint of 54.50 mm. The optimized result showed that there is a significant improvement in the frequency of the mechanism, increasing from an initial design of 53.218 Hz to an optimal design of 75.927 Hz with an improvement of 42.6%. This study provides important reference materials for future research on compliant mechanisms.

Measurements of aerodynamic forces over flapping wings are challenging due to unsteady flowfields and rapidly changing structural loads. This represents an important limitation to the aerodynamic data currently available to researchers working on the aerodynamics of bioinspired flapping wings. This paper proposes the use of pressure-based instrumentation for flapping-wing testing and documents the comparison of two experimental methods to measure the aerodynamic lift generated during the stroke of a rigid flapping wing. The first approach uses a force transducer to measure the forces in air and vacuum, and the second approach uses pressure measurements taken on the surfaces of the wing. The results from both methods are used to validate each other and provide experimental data for a test case with easily simulated conditions. This paper describes the design of the test hardware required, including a custom flap stand, flap mechanics, and instrumented wing construction techniques. A series of flap tests were conducted with pressures measured only in air and force measurements taken both in air and in a vacuum. The data are evaluated with respect to noise, repeatability, and expected scaling trends. The pressure sensor and force transducer measurement strategies are compared based on their accuracy and flexibility.

Compliant mechanisms use the flexibility of the limbs for movement and are produced monolithic, without any conventional joint. These flexible mechanisms have wide applications in several fields such as sensors, grippers, parallel mechanisms, micro-electro-mechanical systems, high-precision devices, and biomedical and surgery robots. Topology optimization is regarded as one of the most frequently used approaches for designing compliant mechanisms. The present study aimed to develop the ground structure approach by meshing the design domain using curved beam elements. Moreover, it seeks to implement three different metaheuristic algorithms, including the genetic algorithm, the imperialist competition algorithm, and the equilibrium optimizer for the topology optimization problem. The structural analysis of the compliant mechanism is necessary for determining the values of the objective functions for the optimization process. In the present study, the finite element method was used to analyze the obtained compliant mechanism. Based on the results, an optimum compliant mechanism with both straight and curved beam elements had better performance compared with a compliant mechanism with only straight beams.

This paper introduces a simple and low cost flapping wing mechanism fabricated monolithically from SUEX dry film, an epoxy based negative photoresist similar to SU-8. The developed process has fewer steps compared to other methods, does not use precious metals, and greatly reduces processing time and cost. It simultaneously defines the PAV airframe, compliant flapping mechanism, and artificial insect wing using photolithography. Rapid prototypes were fabricated with precisely defined features and material properties and geometry that are similar to insects. A linear model with simplified aerodynamics is developed with amplitude dependent damping and validated using experimental results in air and in vacuum. Angles up to 45° at a resonant frequency of 47 Hz are observed that demonstrate applicability of the developed fabrication process for flapping wing air vehicle applications.

This paper outlines the use of a three-dimensional topology optimization scheme for the conceptual design of compliant flapping micro air vehicle mechanisms. Each trilinear finite element within the design domain is assigned to a density variable that smoothly interpolates between 0 (void) and 1 (solid), using a well-known methodology. A mechanism topology is found that converts a series of sinusoidal actuation point loads along the lower surface into a dynamic structural deformation, which in turn provides the desired flapping kinematics. Specifically, a mechanism is desired that can independently control more than one flapping rotation (i.e., flapping and feathering) at the same time.

Flapping wing unmanned air vehicles (UAVs) are small light weight vehicles that typically have short flight times due to the small size of the batteries that are used to power them. During longer missions, the batteries must be recharged. The lack of nearby electrical outlets severely limits the locations and types of missions that these UAVs can be flown in. To improve flight time and eliminate the need for electrical outlets, solar cells can be used to harvest energy and charge/power the UAV. Robo Raven III, a flapping wing UAV, was developed at the University of Maryland and consists of wings with integrated solar cells. This paper aims to investigate how the addition of solar cells affects the UAV. The changes in performance are quantified and compared using a load cell test as well as Digital Image Correlation (DIC). The UAV platform reported in this paper was the first flapping wing robotic bird that flew using energy harvested from on-board solar cells. Experimentally, the power from the solar cells was used to augment battery power and increase operational time.

In order to experimentally validate an aeroelastic modeling tool, a flapping mechanism has been built to flap a flexible wing structure about a single axis. A comparison of the flexible tip deformation during the flapping stroke is of particular interest. Due to the small size of fully-scaled mechanisms, the “commanded” kinematics may differ substantially from what is observed. A crucial input into any numerical flapping wing model, the temporal derivatives of the flapping kinematics, is then not known with certainty. For the current work, the flap rotation is measured with a non-contact image correlation technique, and a Fourier series fit is used to obtain flapping velocities and accelerations. The resulting match between experimental and numerical tip displacements is satisfactory for a very small range of harmonic number. A recommended strategy for future numerical modeling efforts is to include the entire flapping system (power source, actuation, wings) into the framework in order to improve the validation process, with less dependence upon experimental data to “tune” the computational model's input kinematics.

As humans continue to develop the undersea engineering ecosystem of systems, the consequences of catastrophic events must continue to be investigated and understood. Almost every undersea pressure vessel, from pipelines to sensors to unmanned vehicles, has the potential to experience a catastrophic collapse, known as an implosion. This collapse can be caused by hydrostatic pressure or any combination of external loadings from natural disasters to pressure waves imparted by other implosion or explosion events. During an implosion, high-magnitude pressure waves can be emitted, which can cause adverse effects on surrounding structures, marine life, or even people. The imploding structure, known as an implodable volume, can be in a free-field or confined environment. Confined implosion is characterized by a surrounding structure that significantly affects the flow of fluid around the implodable volume. Often, the confining structure is cylindrical, with one closed end and one open end. This work seeks to understand the effect of fluid flow restriction on the physics of implosion inside a confining tube. To do so, a comprehensive experimental study is conducted using a unique experimental facility. Thin-walled aluminum cylinders are collapsed inside a confining tube within a large pressure vessel. High-speed photography and 3D Digital Image Correlation are used to gather structural displacement and velocities during the event while an array of dynamic pressure sensors capture the pressure data inside the confining tube. The results of this work show that by changing the size of the open end, referred to as the flow area ratio, there can be a significant effect on the structural deformations and implosion severity. It also reveals that only certain configurations of holes at the open end of the tube play a role in the dynamic pressure pulse measured at the closed end of the tube. By understanding the consequences of an implosion, designers can make decisions about where these pressure vessels should be in relation to other pressure vessels, critical infrastructure, marine life, or people. In the same way that engineers design for earthquakes and analyze the impact their structures have on the environment around them, contributors to the undersea engineering ecosystem should design with implosion in mind.

Redesigning a flexural joint for metal-based additive manufacturing