# Verification of Industrial Worker Walking Efficiency with Wearable Hip Exoskeleton
## 1 Introduction  
Although walking assist exoskeletons have shown strong growth mainly in the medical rehabilitation of older adults and the disabled, the demand for exoskeletons on industrial sites has also increased significantly in recent years. In particular, interest is growing in wearable exoskeletons to prevent musculoskeletal disorders, to reduce fatigue, and to improve productivity. The scope of application is expanding across industries, for example, in logistics, manufacturing, construction, and services [1, 2]. Industrial workers can perform physical labor more efficiently with the help of exoskeletons. For example, in lifting, transporting, and assembling [3], they can alleviate physical fatigue and improve work efficiency. Additionally, proper support can help prevent disease and injury associated with overstrain [4]. Robotic exoskeleton devices that support the work of industrial workers, depending on the field of application, are divided into upper limbs, lower limbs, and the waist. In particular, lower-extremity systems must aid the hip, knee, or ankle to enable the user to walk or climb stairs [5]. Lower-extremity assistors include multi-joint robotic systems that can control all lower-extremity joints or single-joint robotic systems that control each lower extremity joint separately. A multi-joint robotic system can effectively perform lower extremity movements through the coordinated output from each joint; however, the need to support multiple joints simultaneously can make the system complicated and heavy [5]. Given their advantage of being lighter than the multi-joint robotic systems, single-joint robotic systems are highly usable once their suitability for a purpose is established. Various hip-assistive robotic devices have been developed for physical enhancement using single-joint robotic systems for the lower extremities. The hip joint is a ball-and-socket joint that enables multi-axis movements such as flexion/extension, adduction/abduction, and internal and external rotation [5]. Some researchers have developed systems to assist the hip in the form of cable-driven modules that support multiple degrees of freedom of the hip joint [6], while many others have developed hip-assistive devices that support hip flexion movements. Various power transmission methods have been used to provide joint torque for hip joint flexion. Examples are pooled-webbing actuators [7], cable-driven modules [8; 9; 10], and passive actuators [11; 12]. Lower-limb-assistive exoskeletons that assist walking are already widely used in medical rehabilitation [13; 14; 15]; however, wearable exoskeletons for industrial workers have many limitations, owing to their high price, heavy weight, and uncomfortable fit [5]. Despite incredible advances in exoskeleton technology, exoskeletons are still mostly limited to research labs or used for expensive clinical treatments. The biggest reason for the limited accessibility may be that their complexities result in increased costs, weight, and size. This complexity comes from the requirement for robust exoskeletons that can accurately mimic the complex movements of human limbs and joints [16]. The misalignment between the exoskeleton and user joints causes uncontrolled interaction forces, negatively affecting the wearer's mobility and metabolism [17] and causing discomfort [18]. Because most walking-assistance exoskeletons assist movement with power, they are heavy and rigid, which can interfere with the wearer's natural movement, and often become a burden, particularly when the power is cut off. Consequently, considerable fatigue occurs after wearing the robot, which limits its application to industrial sites or daily life fields that require active physical activity [5; 19]. Therefore, exoskeleton devices that can be applied to industrial sites must be light, flexible, easy to wear, make little noise, and should not interfere with the wearer's movements even when power is cut off. Recently, various lower-limb wearable devices have been developed that reflect these requirements.