Robotic orthosis to assist overhead operations for double hull structure

Abstract

The design of a new robotic orthosis to fully assist various overhead operations in the shipbuilding industry is proposed, and a dynamics simulation and an experimental study are conducted to validate the performance of impedance control of the new orthosis. There are considerable payloads from cables and reaction forces from injection parts during the blasting cleaning and painting in the shipbuilding process, and these can lead to work-related musculoskeletal disorders in the shoulder and elbow joints. Thus, in this research, the entire robotic orthosis designed for the dynamics simulation consists of joints with a total of 6 degrees of freedom (DOF): a 2-DOF shoulder, a 1-DOF elbow, and a 3-DOF wrist. The equations of motion of the designed robotic orthosis have been obtained on the basis of a relative-coordinate formulation. The contact force between the robotic orthosis and the human hand, gravitational force, and the control forces were considered as external forces. The results of the dynamics simulation are significant and show that the transient motions of robotic orthosis can be well controlled by using an impedance control scheme, while the compliance control is able to control only the steady-state motions. The control of transient motions is important because any unexpected impact forces or undesired dynamic behaviours in human–robot interactions may negatively affect both the worker's physical conditions and the quality of the work. Thus, in this research, we validate the suitability of the impedance control scheme in the described applications. Moreover, for simplicity of the experimental study and for considering the minimally required DOF in painting and blasting, only 3-DOF motions were considered in the dynamics simulation in this research. Finally, the obtained experimental results fully support the idea that the impedance control scheme is appropriate to control the robotic orthosis for overhead operations requiring a high degree of accuracy.