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.

Abstract
1. 서 론
2. 시스템 모델링 및 문제정의
    2.1 회전형 전기-유압식 구동기의 기계요소
    2.2 자연 속도 피드백 효과와 기계임피던스
3. 기계임피던스 감소기반 모델 없는토크제어
    3.1 기계임피던스 감소기법
    3.2 기계임피던스 감소에 대한 최적성
    3.3 모델 없는 토크제어와 외란에 대한 강인성
4. 실 험
    4.1 기계임피던스 감소에 대한 최적성
    4.2 토크제어 성능
    4.3 외란에 대한 강인성
    4.4 중력보상 제어
    4.5 컴플라이언스 제어
5. 결 론
References

• 이웅용(POSTECH) | Woongyong Lee
• 정완균(POSTECH) | Wan Kyun Chung Corresponding author