A new inverse kinematics solution method for maintenance snake arm robots based on a grouping control strategy

Abstract

Based on the difference in the drive structure, snake arm robots can be roughly divided into two categories: one adopts the redundant driving and the other with the underactuated. The large number of redundant degrees of freedom gives snake arm robots great flexibility but also increases the difficulty of solving their inverse kinematics. However, the existing inverse kinematics methods are generally not universal for the two distinct categories. Aiming at this issue, a new inverse kinematics solution method is proposed in this paper. Firstly, a flexible grouping strategy is introduced, which can divide the arm's joints into a specified number of groups, thereby accommodating the constraints of underactuated structures and different task requirements of redundant drive structures. However, the motion of joints in the same group is required to be synchronized and consistent, to align with the characteristics of underactuated structures, which also determines the uniqueness of the inverse kinematics solution. By combining this characteristic, the segment of the arm within the joint group can be simplified by using the equivalent principle, and the inverse kinematics of the group are solved through iteration. Further, a forward and backward search mechanism is established to solve the inverse kinematics of the robot. The forward process is used to accomplish the approach of joint groups to the target of the arm. The backward process utilizes the vector method to derive the pose relationship between joint groups to complete their motion coupling. Finally, a series of experiments are carried out to verify the performance of the method. The experimental results show that the method can obtain the inverse kinematics solution of the snake arm robot within the joint angle limitation and achieve a relatively high position accuracy. Even under different grouping strategies, this method also can effectively acquire the solution.