Development of a Prototype Lower Limb Exoskeleton System to Assist Tea Plantation Workers

Abstract

"Ceylon tea" is famous worldwide because of its quality and unique characteristics. At present tea supply to the global market is decreasing and the production rate is dropping. The Sri Lankan tea industry uses selective tea plucking methods in tea harvesting to produce high-quality tea. In the process of tea leave harvesting, the tea workers have to carry loads over 20kg, maintaining awkward postures, and climb steep terrain. These movements cause several health issues. Among that, Spondylolisthesis disease that is affected on the lower part of the backbone is common. This study mainly aims to develop a lower limb exoskeleton system to assist in carrying the heavy load while climbing a terrain up and down. In this study, initially, a biomechanical analysis was carried out to identify a tea worker's lower limb joint forces. The lower limb exoskeleton was functioned with three main functions; supporting and bearing the weight on the back luggage, supporting the forward and lateral walking patterns, and maintaining the system's stability with varying loads on the back luggage. The weight support mechanism has been introduced to support the heavy load on the design and ground it through the system instead of the wearer's body. The developed exoskeleton is an underactuated system in which only the knee joint has been actuated. A Control system has been introduced to synchronize the system motion with the wearer's natural gait pattern. The best components for the exoskeleton were selected by a morphological analysis that takes the study of design requirements and the system's functions into account. The prototype was tested in the laboratory, measuring muscle power wearing and without wearing a lower limb exoskeleton system with 10kgs on the back luggage. The results show that muscle power is reduced after wearing the system. And also, motor torque assists approximately 37% of total knee joint torque.