Control of the Robotic Butterfly by Abdominal and Wings Motions

本文透過機構蝴蝶的設計，探討腹部及翅膀動態對其胸部旋轉動作之影響，並進一步改變流體作用力的方向。實驗觀察蝴蝶拍撲飛行時，腹部呈現規律的上下擺動及翅膀拍撲造成其胸部的旋轉動作(body rotation)，而胸部的旋轉動作被認為與飛行控制有關。 為了解腹部及翅膀動態對胸部旋轉動作之影響，以實驗室枯葉蝶實驗參數與文獻中的動作參數做為機構設計依據，製作出腹部擺動與拍撲動作可以同步的機構蝴蝶。透過機構分別探討腹部動態和拍撲動作對胸部旋轉的影響，發現增加腹部擺動頻率對胸部角度振幅變化不顯著，而增加腹部佔身體重量的比例可以明顯的增加胸部角度振幅。翅膀的後掠使拍撲時能夠額外提供一個改變身體角度的力矩，提高拍翅頻率也能增加此力矩，造成更大的胸部角度振幅。而腹部動態與拍撲動作的交互作用下，身體可以產生與拍撲角度有相位差的俯仰動作，而此具有相位差的俯仰動作進一步能增加升力與推力，在流場中也看到，加上腹部動態確實改變射流的方向。本研究以機構模擬蝴蝶腹部動態，了解腹部動態如何影響胸部角度，改變流體作用力的方向，進而達到控制飛行方向與軌跡。為微型飛行器的控制提供嶄新的觀點。In this work, a robotic butterfly with new control method is created inspired by the flight dynamics of butterflies; the dynamic of the robot and the flow field generated are also scrutinized. The butterflies fly with significant body motion in nature. Their abdomen rotates periodically during flight, and lead to the body angle and wing kinematics change concurrently. Previous studies also suggest that the body motion and flight trajectories are closely integrated. These evidences show that it is highly possible that butterfly able to control their flight modes via abdomen movements, which motivates us to create a butterfly robot with controllable abdominal motion. The body of our robot contains two parts - thorax and abdomen. The joint between them can fold as the real butterfly. The wing span and the weight of the robot are around 50 cm and 330 g, respectively. Two four–linker mechanisms were adopted to achieve flapping and abdominal motion, and were driven by a motor operated at 67 rpm. The mechanism allows the wing and abdomen to move synchronized. We recorded the motion of this robot with a camera by hinging it at the thorax, and then analyzed the interaction among the motions of thorax, wings and abdomen. The flow field generated by the robot were also analyzed with particle image velocimetry (PIV) technique. The results indicate that the abdominal motion largely affects the phase of thorax angle. For the test of the robot without the abdominal motion, the thorax and wing motion are in phase. The robot generates neither lift nor thrust with this motion since the down- and up-stroke jet are generated oppositely. In contrast, when the robot with abdominal motion, the phase of thorax angle is delayed, which is similar to that observed from the real butterflies. The flow field indicates that the directions of jet-flow generated in down- and up- stroke significantly twisted downward and backward, respectively, and are beneficial for robot to generate lift and thrust forces. Our current robot cannot generate enough lift to stay aloft, however, this work reveals the importance of the abdominal motion in the flight control of butterfly, which might be an alternative strategy to control MAVs in the future