중량물 취급용 착용로봇의 무릎관절 가반하중 향상 및 제어에 관한 연구

Abstract

In military and industrial applications, wearable robots must meet the required payload capacity over the entire range of human pilot motion to be able to deal with the heavy loads associated with safety and work-performance issues. The payload capacity of a wearable robot employing rotary actuators or linear actuators at the knee joints decreases drastically in the knee-flexion posture because the moment arm of gravity increases and the moment arm of the force generated by the linear actuators at the knees decreases after a certain point. Furthermore, since variation of the moment arm influences pressure sensing, oscillation can be produced in the knee-flexion posture. Such problems can occur in many joint mechanisms that employ a combination of a linear actuator and a sensor. To resolve this issue, in this study, the author proposes two types of sub-link mechanisms and an elastic mechanism combined with another sub-link mechanism to increase the moment arm of the elastic force in the knee-flexion posture. After only a few modifications to the existing knee-joint configuration, the moment arm of the actuation force in the knee-flexion posture increases. Consequently, the payload capacity increases, enabling robot pilots to squat and stand up with heavy loads. In addition, the author proposes three kinematical and control algorithm methods for reducing oscillation. The kinematical methods involve adjusting the sensor positions from the linear actuator to each joint and fixing the moment arm of the actuator force regardless of the knee joint angle. The control-algorithm-based method involves applying a variable mechanical admittance control gain. Because the proposed mechanisms and methods reduce the effect of the variable moment arm on the wearable robots employing a combination of a linear actuator and a sensor, oscillation is reduced considerably. The proposed mechanisms and methods are simulated and tested using a wearable robot and their effectiveness is verified.