A U-FABRIK Method for Inverse Kinematics of the Rigid-Flexible Serial Robot Working in Narrow Spaces

A uniformed forward and backward reaching inverse kinematics (U-FABRIK) method is proposed for the designed rigid-flexible serial robot with both the rigid mechanism and the flexible mechanism. In this method, both the end pose and overall configuration of the rigid-flexible serial robot can be synchronous planned to perform collision avoidance and joint limit avoidance. The key steps of this method are as follows. Firstly, the 7-DOF rigid mechanism and the 4-DOF flexible mechanism are uniformly simplified into equivalent segments. The lengths and positions of equivalent segments can be solved based on the current configuration of the rigid-flexible serial robot. Secondly, the end roll angle adjustment is added in the equivalent segment iteration process according to characteristics of the rigid-flexible serial robot. This method allows for the complete constraint on the end pose of the rigid-flexible serial robot. Thirdly, the kinematic parameters of the rigid-flexible serial robot are determined by fitting the rigid mechanism and flexible mechanism with equivalent segments. Finally, the prototype of the rigid-flexible serial robot is developed and experimented. The maximum end position error of the rigid-flexible serial robot is no more than 5.7 mm. The results verify the effectiveness of the proposed U-FABRIK method.