Observer-based state estimation of snake-like robot with rotational elastic actuators

The long-term goal of this study is to realize a locomotion control for snake-like robots on various environments. A key point for the locomotion control is the normal direction friction force of each link of the robot. Because, a real snake can locomote by utilizing the difference of frictions in the propulsive and in the normal direction. In previous our study, a locomotion control of the snake-like robot considering side-slipping has been proposed. However, there are some problems to realize the control by a real machine. As the problems, all state of the snake-like robot is supposed to be observed, and computational load of the control law is too large to be real-time. To solve these problems, this paper aims to develop a state estimation of the snake-like robot in consideration of side-slipping by utilizing an observer. Moreover, a rotational elastic actuator consisting of a motor and a spring is installed for the robot to adapt to various environments. Motion equations of the snake-like robot with rotational elastic actuators and side-slipping effect are derived. Constraint forces of the normal direction of each link are also formulated in the modeling process. A type-I observer based on State Dependent Riccati equation: SDRE is utilized to detect a slipping link of the robot. This detection is based on the generalized coordinate of the robot link estimated by the observer. Numerical simulations are given to verify the effectiveness of the proposed method.