This paper presents a study on a compliant cable-driven exoskeleton for hip assistance in lifting tasks that is aimed at preventing low-back pain and injuries in the vocational setting. In the proposed concept, we used twisted string actuator (TSA) to design a light-weight and powerful exoskeleton that benefits from inherent TSA advantages. We have noted that nonlinear nature of twisted strings’ transmission ratio (decreasing with twisting) closely matched typical torque-speed requirements for hip assistance during lifting tasks and tried to use this fact in the exoskeleton design and motor selection. Hip-joint torque and speed required to lift a 10-kg load from stoop to stand were calculated, which gave us a baseline that we used to design and manufacture a practical exoskeleton prototype. Preliminary experimental trials demonstrated that the proposed device was capable of generating required torque and speed at the hip joint while weighing under 6 kg, including battery.
This study presents the design, development, and preliminary evaluation of a lightweight hip exoskeleton utilizing Twisted String Actuators (TSAs) to assist human lifting motions, with a focus on industrial scenarios where workers are subject to repetitive and load-intensive tasks. The core innovation lies in exploiting the TSA’s inherent nonlinear transmission characteristics—specifically, its increasing gear ratio and torque output as the string twists—to match the human hip joint’s torque-speed demands during lifting. Through biomechanical analysis of a 10 kg load-lifting task, the authors identified the required torque and angular velocity profiles of the hip joint, which informed the design of the actuator and transmission system. A single brushless DC motor driving the TSA was selected and configured to achieve the desired range of motion and output force, while maintaining system compactness and portability. The actuator system transmits force through flexible cables attached to a thigh interface, eliminating the need for bulky gearboxes and reducing the total system mass to under 6 kg, including the battery. Experimental results validated that the TSA-based exoskeleton could deliver sufficient torque output and angular motion to assist in lifting without impeding the wearer’s movement. Furthermore, the TSA mechanism demonstrated a favorable alignment between actuator dynamics and biomechanical assistance profiles, suggesting high mechanical efficiency for task-specific assistance. The paper concludes by highlighting the potential of TSA-driven wearable robots for scalable, low-profile assistive applications. It suggests future research directions, including real-time control strategies, human-in-the-loop testing, and integration with biosignal-based intention detection.