부산대학교 도서관

Compression straps are the most commonly used physical human-robot interface element in the wearable robotics field. The main role of the strap is to transmit mechanical power to the wearer by compressing specific body parts and minimizing relative movement. To maximize the robot's functionality through efficient force transmission, high stiffness and tension of the strap are necessary. However, the strap continuously compresses skin tissue while wearing the robot, leading to discomfort and vascular disturbances, thereby compromising the robot's wearability. This paper proposes method of controlling the strap compression force based on the actuation stage of the robot, aiming to address the discomfort caused by prolonged strap compression force. Also, the design method of optimized strap through structural stiffness tuning is introduced to solve the pressure concentration according to the curvature of the body segment and strap shape. First, a preliminary experiment using a hip orthosis was performed to verify the concept of controlling the strap compression force. The proposed strap applied to the hip orthosis is designed to activate the strap compression force by external actuator only when the wearer's hip joint reaches the limited angle of the orthosis during walking. Therefore, the effectiveness of the proposed strap in terms of efficiency and wearability was quantitatively evaluated by comparing following experiments: the wearer’s and orthosis’s hip joint angles, pressure distribution on the contact surface, physiological response due to the state of the strap compression force. As a result, it was confirmed that by periodically adjusting the strap compression force, orthosis was able to fully perform its role with appropriate compression force when necessary, and discomfort caused by continuous pressure was alleviated. Therefore, by verifying the performance and effectiveness, the potential application to walking assistance exoskeleton robots could be confirmed.Next, in terms of design method of optimized strap, a mesh structure design method was applied to control the local stiffness of each section. The pressure at the contact surface between the strap and the body is determined by the amount of deformation and stiffness of the mesh structured strap, mechanical properties and curvature of the skin. To distribute the concentrated pressure, appropriate stiffness must be applied to the mesh structure of the strap in the relevant area. Therefore, optimized design method of the strap is proposed through the experiment to control the local stiffness of the strap. In the experiment, pressure was measured with a uniform mesh strap before the stiffness is controlled for different curvature on the contact surface. Based on the pressure measurement results, the optimal coefficient of stiffness for pressure distribution is derived and an optimized strap is designed. Lastly, pressure measurements were performed again and the result of the pressure distribution and its variance of optimized strap and uniform strap were compared. Experimental results confirmed a decrease in pressure variance for the optimized design, demonstrating the ability to evenly distribute concentrated pressure on the contact surface according to curvature.Lastly, the proposed method of controlling the strap compression force and design method of optimized strap were applied to the previously developed walking assistance exoskeleton robot to implement the active strap. Three experiments were conducted to compare the performance and wearability of an exoskeleton robot equipped with an active strap and a conventional strap. The experiment consisted of a comparing joint trajectory error of the exoskeleton robot and the wearer, pressure distribution on the contact area, and a comparison of qualitative wearability evaluation between active strap and conventional strap. According to the experimental results, in terms of joint trajectory error, the active strap showed similar performance to a conventional strap by properly activating the compression force in the phase where robot power transmission is required. Considering the pressure distribution on the contact surface, the active strap shows that the mean pressure distribution over time is lower than that of the conventional strap, and the variance of the optimized active strap was reduced by 30% compared to the uniform active strap with a uniform mesh structure. Finally, in the qualitative evaluation by the wearer, wearing active strap resulted in less thigh pressure compared to conventional strap, and the active straps showed superior performance in terms of mobility.