Task-space Zero Impedance Control of Three-Degree-of-Freedom Flexible Manipulator based on Disturbance Observer

Collaborative robots are a promising solution to deal with unconstrained environments. Since collaborative robots work with a human in the same space, safety is the biggest obstacle for collaborative robots to settle in the industrial field. The impedance of robots is one of the most decisive factors causing injury and damage in the collision. Zero Impedance Control(ZIC) effectively reduces the reaction forces generated in the event of an impact between a human and a robot by lowering the impedance of the robot. The ZIC with torque sensors in joint has its limitation of safety because of uncontrollable first cycle impact. ZIC with SEA covers the limitation with its own passive compliance. This paper presents the multi-link flexible manipulator with SEA and the configuration is provided. Control architecture based on spring deformation disturbance observer(DOBd) is used for high-performance ZIC of SEA. The task-space controller makes each joint move following coordinated motion in a multi-link system. With three experiments, the effect of the actuator's controller based on DOBd on the performance of joint space ZIC, ZIC in task-space, and safety in the collision is verified.