The flapping wing micro air vehicle (FWMAV) has been attracting lots of interest since the 1990s and is one of the research hotspots in microminiaturization design. However, along with the miniaturization of FWMAV development, flight endurance becomes the bottleneck that significantly impedes the rapid development for these aircrafts because of the critical limit in energy supply due to the limited overall size and weight. In this paper, energy recovery technology was developed for FWMAV with the new type polyvinylidene fluoride (PVDF) piezoelectric wing which could generate the electric potential energy caused by the wing deformation due to the characteristics of the PVDF material. A single crank double rocker mechanism flapping platform was designed to test the deformation energy collection effect and aerodynamic lift. The PVDF wing surface was divided into 16 grid areas to be measured respectively. The lift, output voltage and output power variations for the different flapping frequency was successfully obtained in tests. By analyzing test data, if could be found that the output power could reflect the flutter condition without equipping other sensors and adding extra weight to the aircraft. Moreover, when the flapping frequency was accelerated to 12 Hz, the output power and root mean square (RMS) voltage could increase to 21 μW and 6 V respectively, which is enough to power micro electronic devices such as LED lights.
The surfaces with textures have been widely used as functional surfaces, and the textures are usually generated on flat or cylindrical surfaces. Textured freeform surfaces will have more potential applications. The authors have proposed the double-frequency elliptical vibration cutting (DFEVC) method to machine freeform surfaces on steel materials. Based on this method, a new diamond turning method is developed, in which the variable-frequency modulations are utilized to control the tool marks left on the machined surface to generate the micro/nano dimple textures with high uniformity on the freeform surface. Different from the conventional surface topography model based on the ideal tool cutting edge with zero cutting edge radius, a new modeling approach based on the tool surface profiles is proposed, in which the rake face, the flank face, and the cutting edge surface with actual non-zero cutting edge radius instead of the ideal cutting edge are included for the tool model, the tool surfaces during the machining process are analytically described as a function of the tool geometry and the machining parameters, and the influences of the tool surface profiles on the topography generation of the machined surface are considered. A typical freeform surface is textured on die steel, and the measured results verify the feasibility of the proposed turning method. Compared with the topography prediction results based on the ideal cutting edge, the results considering the tool surfaces show improved simulation accuracy, and are consistent with the experimental results, which validates the proposed topography prediction approach.
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