Nonlinear disturbance observers for robotic continuum manipulators

Abstract

Robots are an indispensable part of modern production lines. Usually working in designated areas, they are separated from human workers in order to avoid collisions. A safe collaborative work environment is enabled by so-called soft robots, which constitute a human-friendly alternative to classical rigid industrial robots. However, modeling soft robots proves difficult and results in a lack of accuracy for control tasks. In this contribution, a disturbance observer-based control is proposed in order to improve tracking behavior. In doing so, unknown model errors are considered as disturbances and estimated by an observer. This estimate is used to actively reject the perturbation. Different disturbance observers are designed and implemented for a soft quasi-continuum manipulator, amongst them two nonlinear disturbance observers and two extended state observers. The distinction in the versions of the same observation concept lies in the disturbance dynamics assumption, which is either considered static or as a damped double integrator. All implemented concepts combined with a PD control show superior performance compared to an existing benchmark concept based on PID-like control. Thanks to the modularity of this approach, disturbance observers can be further investigated in combination with other control strategies.