This study analyzed the duct characteristics of hubless rim-driven propeller (RDP) used in underwater robots. In the previous study, flow visualization experiments were performed with an advancing ratio of 0.2 to 1. The vortex at the front of the duct increased in strength while maintaining its size as the advancing ratio decreased. Therefore, it is necessary to study the optimization of the duct shape. Conventional propeller thrusters use acceleration/deceleration ducts to increase their efficiency. However, unlike conventional propellers, it is impossible to apply to airfoil acceleration/deceleration ducts due to the RDP structure. In this study, duct wake flow characteristics, thrust force, and efficiency according to the duct shape of RDP were analyzed using numerical analysis techniques. Duct design is limited and six duct shapes were designed. As a result, an optimized duct shape was designed considering duct wake flow characteristics, thrust force, and efficiency. The shape that the outlet width of the RDP was kept constant until the end of the duct showed higher thrust force and efficiency.

A retractable bollard system has been used for the traffic control and protection of important facilities such as electric power plants, airports and government buildings etc. The power source of the driving unit of the conventional protective bollard system is on hydraulic or pneumatic system which has several disadvantages compared to an electric driven unit. In this research, an electric driven unit for an automatic retractable bollard is designed and developed to replace the conventional hydraulic and pneumatic driven type. For the reliability test of the developed electric driven unit, a field test has been successfully done. A case study was conducted to develop a defensive retractive bollard which the target performance is 9sec. and 7sec. on its raising and descending operation speed respectively with 750mm in stroke. The required time limit was fully satisfied as the time measured from the experiment were 7.5sec and 5.5sec for each operation. The developed unit also passed 364,000 cycles of operation without any serious malfunctions at the load test proving its reliability. The design theory and process of an electric driven unit of the automatic retractable bollard presented in this article is believed to be very useful contribution and design tool in advancing the physical security industry.

이상과 같이 엑튜에이터의 동특성 해석을 행하고 PID 제어기 및 최적 제어기를 설계하여 응답시뮬레이션을 한 결과 다음과 같은 결론을 얻었다. 1) 엑튜에이터 부의 시정수는 엔진 부의 시정수에 비해 아주 작아 생략하여 제어계를 구성할 수 있다. 2) 한계 감도법에 의해 PID 제어기를 시뮬레이션 한 결과 PID 제어 가버너는 전반적으로 오버슈트가 크고 중속 및 고속 상태에서는 정정시간이 비교적 짧지만 저속에서는 정상 상태에 도달하는데 상당한 시간이 걸린다. 3) 중량 matrix를 적당히 선택하여 최적 피이드 백 게인을 구한 후 마이크로 프로세서에 저장하여 제어기를 구성하면 PID 제어기 보다 양호한 응답 특성을 갖는 제어기를 설계 할 수 있다.

This paper proposes a simple and intuitive model-free torque-tracking control for rotary electro-hydraulic actuators. The undesirable natural-velocity-feedback effect is discussed by introducing mechanical impedance into the electro-hydraulic actuation system. The proposed model-free torque control comprises inner- and outer-loop control to achieve two control objectives. Inner-loop control reduces the mechanical impedance passively and optimally. To improve the tracking accuracy, a certain form of proportional-integral-derivative control is applied to the outer loop. The robustness of the proposed closed-loop system against external disturbances is demonstrated by transforming the two-loop control structure into a disturbance observer form. The proposed method is validated on a single joint electro-hydraulic actuator.