Flapping Wing Mechanisms for Pico Air Vehicles Using Piezoelectric Actuators

Open Access
Author:
Mateti, Kiron
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 14, 2012
Committee Members:
  • Srinivas A Tadigadapa, Dissertation Advisor
  • Christopher Rahn, Dissertation Advisor
  • Zhiwen Liu, Committee Member
  • Qiming Zhang, Committee Member
  • George A Lesieutre, Committee Member
Keywords:
  • MEMS
  • compliant mechanisms
  • piezoelectric actuators
  • flapping wing air vehicles
  • biologically inspired robotics
Abstract:
Swarms of flying robotic insects could revolutionize hazardous environment exploration, search and rescue missions, and military applications. Reducing size to insect scale enables entrance into extremely narrow spaces with inherent stealth advantages. For mass production, these vehicles must have reliable and repeatable fabrication processes that define flapping wing mechanisms with microscale features and produce large flapping amplitudes at frequencies in the range of many insects. This thesis focuses on the design and fabrication processes of flapping wing mechanisms for these types of robots. First, the design, fabrication, modeling, and experimental validation of the Penn State Nano Air Vehicle (PSNAV), a NAV scale piezoelectrically actuated clapping wing mechanism, is presented. A flexure hinge allows passive wing rotation for the clapping wing mechanism. Analytical models of wing flapping and rotation are derived and validated using experimental wing trajectory results. The PSNAV prototype is experimentally shown to provide approximately 54 deg. peak to peak wing rotation, 14 deg. peak to peak flapping angle, and 0.21 mN of thrust at 9.5 Hz. At 25.5 Hz, the prototype produces a maximum of 1.34 mN of thrust. The PSNAV model accurately predicts the wing resonances in the experimental prototype. Model-predicted thrust is lower than the experimentally measured values, however. Towards a compliant mechanism, the next stage of this research introduces a simple process to monolithically fabricate flying robotic insects at the pico air vehicle (PAV) scale 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. Using this process, we designed and fabricated the LionFly, a flapping wing prototype actuated by a PZT-5H bimorph actuator. Several LionFly prototypes were fabricated and experimentally tested. Theoretical and experimental results have excellent agreement validating the compliant mechanism kinematics and aerodynamic added mass and damping. High voltage tests show a peak to peak flapping angle of 55 deg. at 150 V amplitude with 150 V DC offset at 51 Hz resonance. Consistent performance from multiple prototypes demonstrate the reliable and repeatable nature of the fabrication process. Lastly, this research presents detailed modeling and experimental testing of wing rotation and lift in the LionFly. A flexure hinge along the span of the wing allows the wing to rotate in addition to flapping. A linear vibrational model is developed and augmented with nonlinear aerodynamic forces using the blade element method. This model is validated using experimental testing with a laser vibrometer and accurately predicts small amplitude wing dynamics in air and vacuum. Strobe photography and high definition image processing is used to measure high amplitude wing trajectories. At higher amplitudes, the model can sufficiently predict wing trajectory amplitudes, but phase measurement and simulation have slight error. The LionFly produces 46 deg. flap and 44 deg. rotation peak to peak with relative phase of 12 deg., and maximum lift of 71 µN at 37 Hz. By reducing the inertia of the wing and tuning the rotational hinge stiffness, a redesigned device is simulated to produce lift to weight ratio of one.