In this research, a course correction mechanism using multiple on-and-off reciprocating drag brakes and control fins and a bi-stable actuator to drive conceptual fins have been proposed. Typically the drag brakes and control fins are placed mostly inside of the cylindrical body and repeatedly pop out to produce additional control forces and moments until the projectile hits the target. To numerically demonstrate the proposed course correction concepts, the 6-DOF equations of motion are directly integrated to obtain the flight trajectories of the projectile, where the aerodynamic coefficients according to the discrete configurations of the projectile are tabulated by using MISSILE DATCOM. The results of Monte Carlo simulation with randomly perturbed initial flight conditions shows that the proposed projectile equipped with multiple on-and-off reciprocating drag brakes and control fins greatly improves the circular error probable(CEP) from 45.6m in ballistic to 5.6m in controlled and the drag brakes and control fins were repetitively reciprocated with the stroke amplitude of 8mm and 3Hz operating frequency during the flight.
A new two-step amplifying mechanism combining a lever-arm with flexure hinges and a pre-curved thin shell structure is proposed to make a millimeter-scale linear actuator driving the drag brakes and control fins with those amplitude and operating frequency. A large amplification ratio can be obtained by the snap through effect of a post-buckled shell structure without losing actuation force. the snap-through phenomenon of pre-curved thin plate are numerically analyzed by using the ABAQUS to specify the trigger force and displacement required to initiate the snap-through. the analytic results are in good agreement with the test results for the pre-curved shell structure. The trigger force and displacement for snap-through are supplied by the lever-arm with the piezo stack actuator. Amplification ratio of the lever arm is drastically changed according to the external load. the lever arm mechanism is designed to have enough actuation force and displacement to trigger snap-through of the bi-stable structure. The components of the designed actuators are manufactured and integrated. The designed bi-stable actuator is experimentally validated to operate with an 10mm stroke and 13Hz bandwidth.
본 연구에서는 돌출(on)과 후퇴(off)를 반복할 수 있는 항력판을 이용한 탄도수정기구와 항력판 구동을 위한 on-off형 bi-stable 작동기를 제안하였다. 탄의 내부에 수납되는 항력판이 반복적으로 돌출될 때 얻어지는 제어력과 모멘트를 이용하여 재래식 탄의 탄착 정확도를 개선한다. MISSILE DATCOM을 이용하여 항력판 돌출에 따른 탄의 주요 비행형상에 대한 공력자료를 산출하였고 6자유도 비행방정식을 적분하여 탄의 비행궤적을 해석하였다. 다양한 비행환경을 고려한 Monte Carlo해석 결과, 제안된 탄도수정기구는 45.6m였던 탄의 CEP를 5.6m수준으로 크게 개선시키는 효과를 보였다. 이 과정에서 항력판은 최대 작동주파수는 3Hz와 8mm의 돌출거리를 가지고 on-off로만 동작하였다. 항력판의 구동 요구조건을 만족하는 작동기를 구현하기 위하여 레버암과 굽힘변형된 박판구조를 결합한 2단계 변위확대기구를 제안하였다. 박판구조를 굽힘변형시켜 구현한 bi-stable 구조의 스냅스루를 이용하여 on-off거동과 변위확대효과를 얻었으며 레버암형 변위확대기구와 압전작동기를 연결하여 bi-stable구조의 스냅스루에 소요되는 에너지를 공급하였다. 해석 및 실험을 통하여 주요 특성을 확인한 구성품들을 조합하여 10mm의 행정거리와 13Hz의 작동주파수를 가진 bi-stable 작동기를 구현하였다.
