Virtual-work-based optimization design on compliant transmission mechanism for flapping-wing aerial vehicles

This paper presents a method for analyzing and optimizing the design of a compliant transmission mechanism for a flapping-wing aerial vehicle. Its purpose is of minimizing the peak input torque required from a driving motor. In order to maintain the stability of flight, minimizing the peak input torque is necessary. To this purpose, first, a pseudo-rigid-body model was built and a kinematic analysis of the model was carried out. Next, the aerodynamic torque generated by flapping wings was calculated. Then, the input torque required to keep the flight of the vehicle was solved by using the principle of virtual work. The values of the primary attributes at compliant joints (i.e., the torsional stiffness of virtual spring and the initial neutral angular position) were optimized. By comparing to a full rigid-body mechanism, the compliant transmission mechanism with well-optimized parameters can reduce the peak input torque up to 66.0%

ポリマー微細加工によって作成される羽ばたき翼微小飛行体のデザインウィンドウ探索法による開発

The specific flight mechanisms of insects like hovering and maneuverability along with their tiny size nature grasp the attention of many researchers across the globe to utilize the phenomena for the development of biomimetic flapping wing air vehicles which can be used in the wide areas like hazardous environment exploration, rescue, agriculture, pipeline inspection, and earthquake or tsunami disaster management, etc where human access is difficult. Consequently, many researchers have developed flapping wing air vehicles ranging from macro scale to the nanoscale (the largest dimension should be less than or equal to 10 cm) i.e., flapping-wing nano air vehicles (FWNAVs). The research on insect-inspired FWNAVs indicates that FWNAVs generally consist of micro transmission for getting desired flapping motion, a pair of micro wings, an actuator for the power source, and a supporting frame to support the overall structure. Recently, FWNAVs up to a size of 30 mm have been developed based on the insect’s size. However, the evolution of insects indicates that the size of ultimate small insects is about 1 mm. The further miniaturization of current FWNAVs is difficult because of the large assembly of components and complicated mechanical transmission mechanism. Though, there are mainly two difficulties to successfully developing FWNAVs at the scale of mm-size. The first is the manufacturing difficulty because of the very small structure to realize the wing’s complicated motions. The second is the design difficulty because of multisystem and involvement of coupled Multiphysics like fluid-structure interaction (FSI) design. Along with these difficulties other difficulty includes enough lift to drag ratio for hover and thrust for forwarding flight motion due to fluid mechanics at low Reynolds no (Re < 3000). These difficulties can be overcome by developing FWNAVs based on a design window search methodology where a design solution can be obtained for the design problem satisfying all the design requirements. Further fabricating the FWNAVs using advanced engineering technologies such as microelectromechanical systems (MEMS) technologies which seem to be suitable for mm-size prototypes. Computational analysis and design can be utilized for finding the design window search for FWNAVs. The finite element method (FEM) has been the standard choice as a numerical tool for performing the simulation of Multisystem, because of its capabilities to analyze the geometries of complex shapes, detailed analysis of coupled effect, boundary, and initial conditions. The purpose of this study is to develop 10 mm insect-inspired FWNAV using a 2.5-dimensional structure novel approach, iterative design window search methodology, and polymer micromachining. The proposed FWNAV consists of a micro transmission with a support frame, a micro wing, and a piezoelectric bimorph actuator. The novelty of this research includes, (1) the novel transmission mechanism using two parallel elastic hinges based on geometrically nonlinear bending deformation that produces a large rotational displacement from a small translational displacement, (2) the complete 2.5-D structure which can be fabricated using the polymer micromachining technique without any post-assembly (3) the novel design approach or iterative design window (DW) search method using the advanced computational analysis and design. The advantage of the proposed FWNAV over other FWNAVs includes the lowest energy loss due to no post assembly (friction loss is less), reducing total weight, ease in miniaturization, and enough performance without resonance mechanism. In order to develop the proposed FWNAV, firstly I have designed micro transmissions with a support frame and micro wing and later I have designed FWNAV which has been further miniaturized to design 10mm FWNAV using the iterative DW search method. I have also estimated fatigue life arising due to random cyclic stress, which is mostly ignored by the researchers. Computational flight performance of the proposed FWNAV has been evaluated using Multiphysics coupled analysis i.e., fluid-structure interaction analysis where governing equilibrium equation of motion of micro wing and surrounding airflow has been directly solved by finite element methods. The computational flight performance indicates that mean lift force is comparable to the weight of FWNAV which provides that the proposed FWNAV can lift off. The polymer micromachining has been demonstrated by fabricating the transmission which is a key and central component of FWNAV which indicates the feasibility of polymer micromachining for the development of 10 mm FWNAV. Thus, 10 mm flyable FWNAV can be developed which has enough fatigue life.九州工業大学博士学位論文 学位記番号：情工博甲第369号 学位授与年月日：令和4年9月26日1 General Introduction|2 Proposal of 2.5-dimensional one wing transmission for flapping-wing nano air vehicle|3 Iterative design window search for polymer micromachined flapping-wing nano air vehicle|4 Computational flight performance of flapping wing nano air vehicles using fluid-structure interaction analysis|5 Development of flapping-wing nano air vehicle|6 General Conclusion九州工業大学令和4年

Aerodynamic performance of a flyable flapping wing rotor with passive pitching angle variation

The present work was based on an experimental study on the aerodynamic performance of a flapping wing rotor (FWR) and enhancement by passive pitching angle variation (PPAV) associated with powered flapping motion. The PPAV (in this study 10o~50o) was realized by a specially designed sleeve-pin unit as part of a U-shape flapping mechanism. Through experiment and analysis, it was found that the average lift produced by an FWR of PPAV was >100% higher than the baseline model, the same FWR of a constant pitching angle 30o under the same input power. It was also noted that the lift-voltage relationship for the FWR of PPAV was almost linear and the aerodynamic efficiency was also over 100% higher than the baseline FWR when the input voltage was under 6V. The aerodynamic lift or efficiency of the FWR of PPAV can be also increased significantly by reducing the weight of the wings. An FWR model was fabricated and achieved vertical take-off and free flight powered by 9V input voltage. The mechanism of PPAV function provides a feasible solution for aerodynamic improvement of a bio-inspired FWR and potential application to micro-air-vehicles (MAVs)

Dipteran-insect-inspired thoracic mechanism with nonlinear stiffness to save inertial power of flapping-wing flight

This paper presents the design, analysis, and characterization of a compliant thoracic mechanism that saves inertial power for flapping-wing micro air vehicles. Lightweight polyimide film hinges were previously integrated into a compliant flapping-wing mechanism to reduce friction. However, these were not stiff enough to fully recover wing's inertial energy into elastic energy. To store adequate elastic energy using film hinges, we develop a compliant thoracic mechanism with nonlinear stiffness characteristics by mimicking a Dipteran insect's flight thorax. This thoracic mechanism consists of rigid plates and polyimide film hinges connected to form a closed shell structure. It has a nonlinearly increasing stiffness so that it can slow the wings down rapidly toward the end stroke and subsequently help reverse the wings. It demonstrates almost full recovery of inertial power for 10-cm span flapping wings up to 25 Hz. As a result, it only expends 2% of the total mechanical power on inertial power at 25 Hz. In contrast, the rigid-body mechanism with no elastic storage expends 23% of the total mechanical power on inertial power when the same wings beat at the same frequency. With the capability of elastic energy storage, this compliant thoracic mechanism saves power expenditure ranging from 20 up to 30% to produce the same thrust, in comparison with the rigid-body flapping mechanism. This study shows that power saving is effective only if elastic energy storage is well tuned to recover the wing inertial power.Accepted versio