Dual-Loop Controller for Underwater Snake-Like Robot Based on Dynamic Inverse Solution

The underwater snake-like robot consists of a heterogeneous structure with multiple links, providing strong environmental adaptability and enabling flexible movement in complex and confined environments. However, the attitude of an underwater snake-like robot (the feasible range of the angle between the links) is often restricted by narrow terrain, and using a traditional controller without considering its dynamics can easily lead to problems, such as infeasible control inputs and slow system response. In response to this problem, considering a snake-like robot with three links as an example, this study proposes a dual-loop control method based on a dynamic inverse solution [DI-active disturbance rejection controller (ADRC)]. The outer loop analyzes the robot’s dynamic characteristics and applies dynamic inversion to the desired yaw angular acceleration to compute the optimal joint angles for each link. The inner loop embeds an ADRC, which takes the outer-loop control inputs and outputs the joint rotational velocities. Compared to conventional dual-loop ADRC methods that estimate the total system disturbance, DI-ADRC only estimates the residual disturbance between the total system disturbance and the outer-loop inversion result, thereby greatly reducing the computational burden of the extended state observer. The experimental results verified the feasibility of this method for narrow terrain. Compared to the traditional controller, DI-ADRC has smaller overshoot and oscillation, significantly improving control accuracy and response speed, and can dynamically reduce or increase the time to reach the target attitude.